研究者詳細 - 池田　直

論文 - 池田　直

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Ginzburg-Landau action and polarization current in an excitonic insulator model of electronic ferroelectricity

Hiroto Adachi, Naoshi Ikeda, Eiji Saitoh

Physical Review B 107 ( 15 ) 2023年4月

ファイバーエアロゾルデポジション法によるバインダーレス炭素短繊維構造体の成形査読

森正和, 森章太郎, 西川雅仁, 池田直

実験力学 22 ( 4 ) 255 - 259 2023年1月

Direct evidence of electronic ferroelectricity in YbFe<inf>2</inf>O<inf>4</inf> using neutron diffraction and nonlinear spectroscopy

K. Fujiwara, Y. Fukada, Y. Okuda, R. Seimiya, N. Ikeda, K. Yokoyama, H. Yu, S. Koshihara, Y. Okimoto

Scientific Reports 11 ( 1 ) 2021年12月

掲載種別：研究論文（学術雑誌）

We report the first observation of room temperature spontaneous electric polarization in an electronic ferroelectric material, a YbFe2O4 single crystal. The observation was based on second harmonic generation (SHG), a nonlinear optical process. Tensor analysis of the SHG signal revealed that this material has a polar charge superstructure with Cm symmetry. This result settles the long-term discussion on the uncertainty about electronic ferroelectric properties, including the charge order structure. We present a complete picture of the polar charge ordering of this material via consistent results from two different characterization methods. The SHG signal shows the same temperature dependence as the superlattice signal observed in neutron diffraction experiments. These results prove ferroelectric coupling to electron ordering in YbFe2O4, which results in electronic ferroelectricity which is enabled by the real space ordering of iron cations with different valences. The existence of electronic ferroelectricity holds promise for future electronics technologies where devices run a thousand times faster than frequency of the present CPU (a few gigahertz) embedded in smartphones, etc.

DOI： 10.1038/s41598-021-83655-6

Present status of the experimental aspect of RFe2O4 study

Naoshi Ikeda, Tomoko Nagata, Jun Kano, Shigeo Mori

JOURNAL OF PHYSICS-CONDENSED MATTER 27 ( 5 ) 2015年2月

記述言語：英語出版者・発行元：IOP PUBLISHING LTD

We give a brief review of the experimental research on a triangular mixed valence iron oxide RFe2O4 (R = Y, Dy, Ho, Er, Tm, Yb, Lu, Sc or In). Interest in this material has been increasing every year because of the fascinating but complicated interaction between spin, charge and the orbital state of iron ions in frustrated geometry. Reports collected in this review cover experimental research on crystallography, chemical analysis, bulk and thin film preparation, magnetic, dielectric, diffraction with neutrons, x-ray and electron, optical and x-ray absorption, Mossbauer spectroscopy and other methods that incorporate the use of modern scientific technology and knowledge. The report mainly focuses on experimental facts since 1990 on which an early review by Siratori has been published (Kimizuka et al 1990 Handbook on the Physics and Chemistry of Rare Earths vol 13, ed K A Gschneidner Jr and L Eyring

DOI： 10.1088/0953-8984/27/5/053201

Superconductivity in alkali-metal-doped picene

Ryoji Mitsuhashi, Yuta Suzuki, Yusuke Yamanari, Hiroki Mitamura, Takashi Kambe, Naoshi Ikeda, Hideki Okamoto, Akihiko Fujiwara, Minoru Yamaji, Naoko Kawasaki, Yutaka Maniwa, Yoshihiro Kubozono

NATURE 464 ( 7285 ) 76 - 79 2010年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

Efforts to identify and develop new superconducting materials continue apace, motivated by both fundamental science and the prospects for application. For example, several new superconducting material systems have been developed in the recent past, including calcium-intercalated graphite compounds(1), boron-doped diamond(2) and-most prominently-iron arsenides such as LaO(1-x)F(x)FeAs (ref. 3). In the case of organic superconductors, however, no new material system with a high superconducting transition temperature (T(c)) has been discovered in the past decade. Here we report that intercalating an alkali metal into picene, a wide-bandgap semiconducting solid hydrocarbon, produces metallic behaviour and superconductivity. Solid potassium-intercalated picene (K(x)picene) shows T(c) values of 7K and 18 K, depending on the metal content. The drop of magnetization in Kxpicene solids at the transition temperature is sharp (<2 K), similar to the behaviour of Ca-intercalated graphite(1). The Tc of 18K is comparable to that of K-intercalated C(60) (ref. 4). This discovery of superconductivity in K(x)picene shows that organic hydrocarbons are promising candidates for improved T(c) values.

DOI： 10.1038/nature08859

An organic thyristor

F Sawano, Terasaki, I, H Mori, T Mori, M Watanabe, N Ikeda, Y Nogami, Y Noda

NATURE 437 ( 7058 ) 522 - 524 2005年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

Thyristors are a class of nonlinear electronic device that exhibit bistable resistance - that is, they can be switched between two different conductance states(1). Thyristors are widely used as inverters ( direct to alternating current converters) and for the smooth control of power in a variety of applications such as motors and refrigerators. Materials and structures that exhibit nonlinear resistance of this sort are not only useful for practical applications: they also provide systems for exploring fundamental aspects of solid- state and statistical physics. Here we report the discovery of a giant nonlinear resistance effect in the conducting organic salt(2) theta- ( BEDT- TTF) 2CsCo( SCN)(4), the voltage- current characteristics of which are essentially the same as those of a conventional thyristor. This intrinsic organic thyristor works as an inverter, generating an alternating current when a static direct- current voltage is applied. Whereas conventional thyristors consist of a series of diodes ( their nonlinearity comes from interface effects at the p- n junctions), the present salt exhibits giant nonlinear resistance as a bulk phenomenon. We attribute the origin of this effect to the current-induced melting of insulating charge- order domains, an intrinsically non- equilibrium phenomenon in the sense that ordered domains are melted by a steady flow.

DOI： 10.1038/nature04087

Ferroelectricity from iron valence ordering in the charge-frustrated system LuFe2O4

Naoshi Ikeda, Hiroyuki Ohsumi, Kenji Ohwada, Kenji Ishii, Toshiya Inami, Kazuhisa Kakurai, Youichi Murakami, Kenji Yoshii, Shigeo Mori, Yoichi Horibe, Hijiri Kitô

Nature 436 ( 7054 ) 1136 - 1138 2005年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

Ferroelectric materials are widely used in modern electric devices such as memory elements, filtering devices and high-performance insulators. Ferroelectric crystals have a spontaneous electric polarization arising from the coherent arrangement of electric dipoles (specifically, a polar displacement of anions and cations). First-principles calculations and electron density analysis of ferroelectric materials have revealed that the covalent bond between the anions and cations, or the orbital hybridization of electrons on both ions, plays a key role in establishing the dipolar arrangement. However, an alternative model-electronic ferroelectricity-has been proposed in which the electric dipole depends on electron correlations, rather than the covalency. This would offer the attractive possibility of ferroelectric materials that could be controlled by the charge, spin and orbital degrees of freedom of the electron. Here we report experimental evidence for ferroelectricity arising from electron correlations in the triangular mixed valence oxide, LuFe 2O4. Using resonant X-ray scattering measurements, we determine the ordering of the Fe2+ and Fe3+ ions. They form a superstructure that supports an electric polarization consisting of distributed electrons of polar symmetry. The polar ordering arises from the repulsive property of electrons-electron correlations-acting on a frustrated geometry.

DOI： 10.1038/nature04039

Synthesis of Carbon Nanowalls using Plasma-Irradiated Solid Carbon and Absorption of Cs in Water

Yukimasa Fukada, Yumito Aoyagi, Misaki Yokoyama, Yoichi Horibe, Jun Kano, Miyu Kaneda, Tatsuo Fujii, Akitaka Yoshigoe, Masaaki Kobata, Tatsuo Fukuda, Kenji Yoshii, Naoshi Ikeda

Journal of Electronic Materials 54 ( 1 ) 686 - 692 2024年11月

Ultrafast anisotropic polarization dynamics of electronic ferroelectric <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>LuFe</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math>

H. Yu, Y. Fukada, G. Nishida, K. Takubo, T. Ishikawa, S. Koshihara, N. Ikeda, Y. Okimoto

Physical Review Materials 8 ( 6 ) 2024年6月

Structural Characterization of Graphite Analogue BC_x Synthesized Under Various Conditions and Its Application to Ti Intercalation

Kazumasa Horigane, Masayuki Tadokoro, Ritsuko Eguchi, Hirofumi Ishii, Shinichi Nakamura, Takashi Kambe, Naoshi Ikeda, Hidenori Goto, Yoshihiro Kubozono, Jun Akimitsu

Inorganic Chemistry 62 ( 48 ) 19466 - 19473 2023年11月

Nonlinear Optical Properties in an Epitaxial YbFe₂O₄ Film Probed by Second Harmonic and Terahertz Generation 査読国際誌

Hongwu Yu, Yoichi Okimoto, Atsuya Morita, Shuhei Shimanuki, Kou Takubo, Tadahiko Ishikawa, Shin-ya Koshihara, Ryusei Minakami, Hirotake Itoh, Shinichiro Iwai, Naoshi Ikeda, Takumi Sakagami, Mayu Nozaki, Tatsuo Fujii

Materials 16 ( 5 ) 1989 - (1-11) 2023年2月

Valence control of charge and orbital frustrated system YbFe2O4 with electrochemical Li+ intercalation

S. Murase, Y. Yoshikawa, K. Fujiwara, Y. Fukada, T. Teranishi, J. Kano, T. Fujii, Y. Inada, M. Katayama, K. Yoshii, T. Tsuji, D. Matsumura, N. Ikeda

Journal of Physics and Chemistry of Solids 162 110468 - 110468 2022年3月

掲載種別：研究論文（学術雑誌）出版者・発行元：Elsevier BV

We report an attempt valence control of the mixed valence iron triangular oxide YbFe2O4 to develop an effective technique controling the frustration of charges in strongly correlated electron systems. The electrochemical doping of Li + into YbFe2O4 was examined on a cell-type sample similar to the Li-ion secondary battery cell. Systematic changes in the lattice constant and Fe – Fe and Fe–Yb distance were observed with Li doping. Maximum value of the doping was over 300 mAh/g. An EXAFS experiment indicated that Li positioned between Yb octahedron layer (U-layer) and Fe-bipyramidal layer (W-layer). However, detailed change of iron valence state of YbFe2O4was not clearly observed because of the superimpose of the signal from iron metal nano particles in XANES observation. We discuss that the uncertainty might arise from the inhomogeneous distribution of the sample particle size, which might prevent the homogeneous doping of Li because the doping occurs on the surface of each nano-particles.

DOI： 10.1016/j.jpcs.2021.110468

Observation of magnetoelectric effect of charge-ordered ferroelectric LuFe<inf>2</inf>O<inf>4</inf> by inverse capacitance analysis

Yukimasa Fukada, Naoshi Ikeda

Journal of the Physical Society of Japan 90 ( 11 ) 2021年11月

掲載種別：研究論文（学術雑誌）

We report the magnetic field effect on the dielectric constant of the charge-ordered ferroelectric LuFe2O4. Below the Néel temperature of 240 K, we found decreases in capacitance and resistance by the magnetic field. The variation in dielectric constant with the magnetic field was investigated by inverse complex capacitance analysis with a series of equivalent electric circuits having a log-normal distribution of the relaxation time. The phenomenon can be explained by the spin- and charge-ordered domain model, in which the entropy of Fe spins affects the arrangement of Fe charges.

DOI： 10.7566/JPSJ.90.113705

Quantum Interference of Totally Reflected Mössbauer γ-Rays from a 57Fe Monolayer Embedded in a Thin Film

Kosuke Fujiwara, Takaya Mitsui, Yumito Aoyagi, Yoshitaka Yoda, Naoshi Ikeda

Journal of the Physical Society of Japan 90 ( 8 ) 084705 - 084705 2021年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Society of Japan

Total reflection gamma-ray resonant spectra of a Cr/Fe/Cr/MgO thin film in which a Fe-57 monolayer was embedded at a depth of 6 nm below the surface were studied using a synchrotron Mossbauer source. Due to an interference between electron and nuclear resonant scatterings, the spectra showed asymmetric absorption and scattering profiles depending on beam incidence angles. The spectra were reproduced via theoretical simulations based on an anomalous scattering factor associated with nuclear resonance. The origin of the asymmetric spectral profiles was explained by a change in the phase factor of nuclear resonant scattering amplitude at the Fe-57 enriched monolayer. These results pave the way for advanced local magnetic analyses on the deeply buried interface of functional magnetic thin films and direct phase determination of gamma-rays in thin films.

DOI： 10.7566/jpsj.90.084705

Single domain growth and charge ordering of epitaxial YbFe2O4 films

Takumi Sakagami, Reika Ota, Jun Kano, Naoshi Ikeda, Tatsuo Fujii

CRYSTENGCOMM 2021年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ROYAL SOC CHEMISTRY

YbFe<INF>2</INF>O<INF>4</INF> is a charge-ordered ferroelectric that exhibits coupling between magnetization and electric polarization near room temperature and crystallizes in a rhombohedral structure (R3m). This study presents an attempt to fabricate stoichiometric and epitaxial YbFe<INF>2</INF>O<INF>4-delta</INF> films with a nearly single-domain structure using an RF magnetron sputtering method. The (0001)-oriented epitaxial films of YbFe<INF>2</INF>O<INF>4-delta</INF> on YSZ (111) substrates via reactive sputtering method exhibited clear three-fold symmetry normal to the substrate without the formation of twin domains rotated by 60 degrees. The oxygen stoichiometry of the epitaxial YbFe<INF>2</INF>O<INF>4-delta</INF> was improved by controlling an oxygen partial pressure (P<INF>O<INF>2</INF></INF>) during the deposition. The films showed a sharp ferrimagnetic transition, and the transition temperature (T<INF>N</INF>) increased linearly to approximately 245 K with decreasing P<INF>O<INF>2</INF></INF>. The magnitude of magnetization of the obtained films was comparable to that of bulk single crystals. Further, the electron diffraction pattern of the stoichiometric films confirmed the presence of three-dimensional charge order, which is consistent with the behavior of the bulk crystals as well.

DOI： 10.1039/d1ce00834j

High valence states of Pd supported on ferroelectric BaTiO3 driven by electric polarization

Tasuku Yoshida, Jun Kano, Masaichiro Mizumaki, Yusuke Tamenori, Kiyofumi Nitta, Kazuo Kato, Satoshi Hinokuma, Norihiro Oshime, Satoshi Hirose, Hitoshi Mikami, Naoshi Ikeda, Tatsuo Fujii, Yuta Nishina, Tomoko Okubo

APPLIED PHYSICS LETTERS 119 ( 9 ) 2021年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AIP Publishing

At a metal-ferroelectric junction, it has been considered that the electric polarization of the ferroelectric material can affect the electronic structure of the neighboring metal. Here, we demonstrate that the valence state of Pd can be shifted to the unstable high value of 4+ by the electric field of electric polarization in ferroelectric BaTiO3. Study of the absorption fine structure of both hard and soft x rays revealed the existence of Pd4+ states on the surface of Pd oxide nanoparticles. The positions of Pd and oxygen atoms are shifted in opposite directions by the electric field due to the electric polarization of ferroelectric BaTiO3. The atomic displacement of Pd and O forms a zigzag structure, in which the coordination number of Pd atoms is changed from four to six, producing a quadrivalent state. This report presents experimental evidence that ferroelectric polarization can control the electronic states of neighboring metal atoms, and we suggest that using the ferroelectric support effect may produce a new type of catalyst.

DOI： 10.1063/5.0066289

Light reflectance and photoelectron yield spectroscopy enable acceptor level measurement in p-type Ba1-xTiO3 semiconductor

Saya Fujii, Jun Kano, Norihiro Oshime, Tohru Higuchi, Yuta Nishina, Tatsuo Fujii, Naoshi Ikeda, Hiromi Ota

JOURNAL OF APPLIED PHYSICS 129 ( 8 ) 2021年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

We report the band structure of Ba-deficient BaTiO3 as a p-type semiconductor, studied by a combination of light reflectance and photoelectron yield spectroscopy. Two acceptor levels were observed at the tail of a valence band. As the quantity of Ba vacancies increased, the density of state of the two acceptor levels also increased. The levels of the conduction band minimum and the valence band maximum shifted far away from the vacuum level, but the bandgap seems to be independent of Ba deficient concentration. For classical semiconductors such as Si and GaAs, the observation of impurity levels is restricted to low temperatures (similar to 20K) owing to their narrow bandgaps. Oxide semiconductors have now been demonstrated with wide bandgaps and acceptor levels, at normal operating temperatures, which could lead to new device designs in the future.

DOI： 10.1063/5.0033761

Crystallographical and morphological changes in charge-ordering transition of RFe<inf>2</inf>O<inf>4</inf> (R: Y, Lu) investigated by transmission electron microscopy

Y. Horibe, S. Mori, N. Ikeda, K. Yoshii, H. Maeno, Y. Murakami

Ferroelectrics 584 ( 1 ) 20 - 30 2021年

掲載種別：研究論文（学術雑誌）

Temperature dependence of charge-ordered crystal structures and domain structures in RFe2O4 (R: Y and Lu) was investigated by energy-filtered transmission electron microscopy, combined with conventional transmission electron microscopy. The presence of three-dimensional to two-dimensional charge ordering transition were observed in both YFe2O4 and LuFe2O4 on heating. Furthermore, real-space images obtained with the energy-filtered transmission electron microscopy revealed that YFe2O4 has less anisotropic nanometer-scale charge-ordered domains than LuFe2O4. These findings in RFe2O4 indicate the importance of the interchange interactions between Fe-O bilayers in addition to those within bilayers in the structural phase transitions associated with charge ordering in this system.

DOI： 10.1080/00150193.2021.1984762

Analysis of glass behavior of lu<inf>2</inf>fe<inf>3</inf>o<inf>7</inf> with distributed equivalent circuit model

Yukimasa Fukada, Ryota Fukuyama, Kosuke Fujiwara, Kenji Yoshii, Kei Shigematsu, Masaki Azuma, Naoshi Ikeda

Journal of the Physical Society of Japan 90 ( 2 ) 2021年

掲載種別：研究論文（学術雑誌）

We report an analysis of the dielectric glasslike state of the spin- and charge-ordered system Lu2Fe3O7, which has structural and physical properties analogous to those of the electronic ferroelectrics RFe2O4 (R: rare earth). Aging and memory effects of resistivity were found in the electric impedance response. We performed a numerical analysis with equivalent electric circuits that have a logarithmic Gaussian distribution of resistance and capacitance. The distribution parameters well explained the glassy nature of the electric and dielectric properties between 100 and 200 K and the distribution variations of charge- and magnetic-ordered domains underlying the glass nature.

DOI： 10.7566/JPSJ.90.024710

Skewed electronic band structure induced by electric polarization in ferroelectric BaTiO3

Norihiro Oshime, Jun Kano, Eiji Ikenaga, Shintaro Yasui, Yosuke Hamasaki, Sou Yasuhara, Satoshi Hinokuma, Naoshi Ikeda, Pierre-Eymeric Janolin, Jean-Michel Kiat, Mitsuru Itoh, Takayoshi Yokoya, Tatsuo Fujii, Akira Yasui, Hitoshi Osawa

SCIENTIFIC REPORTS 10 ( 1 ) 2020年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE RESEARCH

Skewed band structures have been empirically described in ferroelectric materials to explain the functioning of recently developed ferroelectric tunneling junction (FTJs). Nonvolatile ferroelectric random access memory (FeRAM) and the artificial neural network device based on the FTJ system are rapidly developing. However, because the actual ferroelectric band structure has not been elucidated, precise designing of devices has to be advanced through appropriate heuristics. Here, we perform angle-resolved hard X-ray photoemission spectroscopy of ferroelectric BaTiO3 thin films for the direct observation of ferroelectric band skewing structure as the depth profiles of atomic orbitals. The depth-resolved electronic band structure consists of three depth regions: a potential slope along the electric polarization in the core, the surface and interface exhibiting slight changes. We also demonstrate that the direction of the energy shift is controlled by the polarization reversal. In the ferroelectric skewed band structure, we found that the difference in energy shifts of the atomic orbitals is correlated with the atomic configuration of the soft phonon mode reflecting the Born effective charges. These findings lead to a better understanding of the origin of electric polarization.

DOI： 10.1038/s41598-020-67651-w

Dielectric and magnetocaloric study of TmCrO<inf>3</inf>

K. Yoshii, Naoshi Ikeda

Journal of Alloys and Compounds 804 364 - 369 2019年10月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2019 Elsevier B.V. Dielectric and magnetocaloric measurements are carried out for the chromite TmCrO3. This oxide was reported to be multiferroic below the Néel temperature (TN) of ∼125 K, likely due to a structural transformation. The dielectric response shows large dielectric constants below 300 K. However, from the analyses of loss tangent, AC conductivity and dielectric modulus, this behavior is rooted in hopping of charge carriers rather than electric dipoles, as proposed for some other chromites. No dielectric anomaly is found at TN. The magnetocaloric effect shows that the magnetic transitions at TN as well as the spin reorientation temperature are of a second order. This result strongly suggests the absence of magnetostructural transition at TN in accord with no observation of ferroelectric transition at this temperature.

DOI： 10.1016/j.jallcom.2019.06.359

One-Minute Joule Annealing Enhances the Thermoelectric Properties of Carbon Nanotube Yarns via the Formation of Graphene at the Interface 査読

Masaki Hada, Taisuke Hasegawa, Hirotaka Inoue, Makito Takagi, Kazuki Omoto, Daiki Chujo, Shogo Iemoto, Taihei Kuroda, Taiga Morimoto, Takuma Hayashi, Toru Iijima, Tomoharu Tokunaga, Naoshi Ikeda, Kazuhiro Fujimori, Chihiro Itoh, Takeshi Nishikawa, Yoshifumi Yamashita, Toshihiko Kiwa, Shin-ya Koshihara, Satoshi Maeda, Yasuhiko Hayashi

ACS APPLIED ENERGY MATERIALS 2 ( 10 ) 7700 - 7708 2019年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

Interfaces in nanocarbon materials are highly important, as they determine the properties of carbon-based devices. In terms of carrier and thermal transport properties, the interfacial features are often more important than the intrinsic characteristics. Herein, we describe how 1 min Joule annealing of carbon nanotube (CNT) yarns can convert the interfacial amorphous carbon into graphene fragments. After 1 min Joule annealing, we have obtained multiwalled CNT yams with extremely high Seebeck coefficients (+/- 100 mu V/K) and high thermoelectric power factor (400 and 1000 mu W/mK(2)) at room temperature, both with or without polyethylenimine doping. Theoretical simulations and experimental measurements helped to determine the optimal annealing conditions in terms of a rapid transformation of the interfacial amorphous carbon between the bundled CNTs in the yarn into graphene fragments at similar to 2000 K. The present approach represents significant progress in energy materials science, as it provides a guiding principle for the design of interfaces in nanocarbon materials with potential applications in energy-harvesting systems.

DOI： 10.1021/acsaem.9b01736

Stabilization of spin and charge ordering in stoichiometric YbFe<inf>2</inf>O<inf>4</inf>

Kosuke Fujiwara, Tomoyuki Karasudani, Kazuhisa Kakurai, Wai Tung Lee, Kirrily C. Rule, Andrew J. Studer, Naoshi Ikeda

Journal of the Physical Society of Japan 88 ( 4 ) 2019年

掲載種別：研究論文（学術雑誌）

We report a wide-range reciprocal space observation with neutron diffraction in an iron vacancy controlled YbFe2O4 crystal, which is proposed as a prototype of electronic ferroelectrics arising from iron charge ordering. The increase of the charge ordering transition temperature and the disappearance of spin competitive transition were discovered in this stoichiometric crystal. We suppose that the lower ionic deficiency of this crystal enhances the development of spin and charge order coherence length, and consequently, the intrinsic nature of spin and charge ordering of YbFe2O4 could be detected. The experiment was performed with a two-dimensional neutron detector, and all super-lattice spots and its modulations above magnetic ordering temperature TN = 245 K are successfully explained with six domains of a monoclinic charge-order super-lattice cell. A rather extended two dimensional (2D) spin correlation above TN was identified with polarized 3He neutron spin filter and we found a clear indication of a coupling between the 2D spin correlation and charge ordering between TN and 300 K, at which a new lattice distortion phase may set in.

DOI： 10.7566/JPSJ.88.044701

酸化物に接合された金属薄膜への分子吸着挙動

狩野旬, 押目典宏, 廣瀬哲, 上田剛慈, 安井伸太郎, 浜嵜容丞, 伊藤満, 三上仁志, 池田直, 藤井達生, 柏原浩大

日本物理学会講演概要集 74.2 2103 - 2103 2019年

Modulation in charge ordering structure of ferroelectric YbFe<inf>2</inf>O<inf>4</inf> by magnetic ordering

T. Nagata, N. Ikeda

AIP Advances 8 ( 7 ) 2018年7月

掲載種別：研究論文（学術雑誌）

We report the modulation in charge ordering structure of ferroelectric YbFe2O4 by magnetic ordering from x-ray diffraction experiments and magnetic measurements. The incommensurate modulation was observed on (n n 3m+3/2) type diffraction signal around magnetic ordering temperature where n and m are integer. The modulation was also observed on charge ordering signal, indicating spin-charge coupling. The incommensurate modulation was observed only on (n/3 n/3 3m) type charge ordering signal. This selectivity can be explained by polar charge ordering models.

DOI： 10.1063/1.5026921

Growth and charge ordering of epitaxial YbFe2O4 films on sapphire using Fe3O4 buffer layer 査読

Fujii Tatsuo, Numata Tomoya, Nakahata Hiroki, Nakanishi Makoto, Kano Jun, Ikeda Naoshi

JAPANESE JOURNAL OF APPLIED PHYSICS 57 ( 1 ) 2018年1月

可搬型核モノクロメータの開発と応用

藤原孝将, 三井隆也, 櫻井吉晴, 池田直

日本物理学会講演概要集 73.2 530 - 530 2018年

Crystal-Site-Selective Spectrum of Fe3BO6 by Synchrotron Mossbauer Diffraction with Pure Nuclear Bragg Scattering

Shin Nakamura, Takaya Mitsui, Kosuke Fujiwara, Naoshi Ikeda, Masayuki Kurokuzu, Susumu Shimomura

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 ( 8 ) 2327 - 2336 2017年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We have succeeded in obtaining the crystal-site-selective spectra of the collinear antiferromagnet Fe3BO6 using a synchrotron Mossbauer diffractometer with pure nuclear Bragg scattering at SPring-8 BL11XU. Well-resolved 300, 500, and 700 reflection spectra, having asymmetric line shapes owing to the higher-order interference effect between the nuclear energy levels, were quantitatively analyzed using a formula based on the dynamical theory of diffraction. Reasonable hyperfine parameters were obtained. The intensity ratio of Fe1 to Fe2 subspectra is in accordance with the nuclear structure factor. However, when the spectrum is measured at the peak position of the rocking curve (very near the Bragg position), the value of the center shift deviates from its intrinsic value. This is also due to the dynamical effect of.-ray diffraction. To avoid this problem, it is necessary to use diffraction angles near the foot of the rocking curve, approximately 0.02 degrees apart from the peak position.

DOI： 10.7566/JPSJ.86.084701

Phase relations in the pseudobinary systems RAO(3)-R2Ti2O7 (R: rare earth element and Y, A: Fe, Ga, Al, Cr and Mn) and syntheses of new compounds R(A(1-x)Ti(x))O3+x/2 (2/3 <= x <= 3/4) at elevated temperatures in air

Francisco Brown, Ivan Jacobo-Herrera, Victor Alvarez-Montano, Noboru Kimizuka, Keiji Kurashina, Yuichi Michiue, Yoji Matsuo, Shigeo Mori, Naoshi Ikeda, Felipe Medrano

JOURNAL OF SOLID STATE CHEMISTRY 251 131 - 142 2017年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE

Phase relations in the pseudo-binary systems RFeO3-R2Ti2O7 (R: Lu, Ho and Dy), RGaO3-R2Ti2O7 (R: Lu and Er), LuAlO3-Lu2Ti2O7 and RAO(3)-R2Ti2O7 (R: Lu and Yb. A: Cr and Mn) at elevated temperatures in air were determined by means of a classic quenching method. There exist Lu(Fe1-xTix)O3+x/2, R(Ga1-xTix)O3+x/2 (R: Lu and Er) and Lu(Al1-xTix)O3+x/2 (2/3 <= x <= 3/4) having the Yb(Fe1-xTix)O3+x/2-type of crystal structure (x=0.72, space group: R3m, a(angstrom)=17.9773 and c(angstrom)=16.978 as a hexagonal setting) in these pseudo binary systems. Eighteen compounds R(A(1-x)Ti(x))O3+x/2 (R: Lu-Sm and Y, A: Fe, Ga and Al) were newly synthesized and their lattice constants as a hexagonal setting were measured by means of the X-ray powder diffraction method. The R occupies the octahedral site and both A and Ti does the trigonalbipyramidal one in these compounds. Relation between lattice constants for the rhombic R(A(1-x)Ti(x))O3+x/2 and the monoclinic In(A(1-x)Ti(x))O3+x/2 are as follows, ah approximate to 5 x b(m), ch approximate to 3 x c(m) x sin beta and a(m)=3(1/2) x b(m), where ah and ch are the lattice constants as a hexagonal setting for R(A(1-x)Ti(x))O3+x/2 and a(m), b(m), cm and beta are those of the monoclinic In(A(1-x)Ti(x))O3+x/2. Crystal structural relationships among a-InGaO3 (hexagonal, high pressure form, space group: P63/mmc), InGaO3 (rhombic, hypothetical), (RAO(3))(n)(BO)(m) and RAO(3)(ZnO)(m) (R: Lu-Ho, Y and In, A: Fe, Ga, and Al, B: divalent cation element, m, n: natural number), the orthorhombic-and monoclinic In(A(1-x)Ti(x))O3+x/2 (A: Fe, Ga, Al, Cr and Mn) and the hexagonal-and rhombic R(A(1-x)Ti(x))O3+x/2 (R: Lu-Sm and Y, A: Fe, Ga and Al) are schematically presented. We concluded that the crystal structures of both the alpha-InGaO3 (high pressure form, hexagonal, space group: P63/mmc) and the hypothetical InGaO3 (rhombic) are the key structures for constructing the crystal structures of these compounds having the cations with CN=5.

DOI： 10.1016/j.jssc.2017.04.001

Coherent X-ray diffraction for domain observation II 査読

K. Ohwada, D. Shimizu, J. Mizuki, J. Mizuki, K. Fujiwara, T. Nagata, N. Ikeda, H. Ohwa, N. Yasuda, K. Namikawa

Ferroelectrics 513 ( 1 ) 16 - 21 2017年6月

掲載種別：研究論文（国際会議プロシーディングス）

© 2017 Taylor & Francis Group, LLC. The CXD method have been shown to be applicable to the crystal characterization as well as the domain observation. The present CXD technique could evaluate the crystal coherence length up to 10 μm and the wide variety of samples were chosen in this study. We have shown how the ideal Bragg reflection deforms as the disorder and the defects increases and form the speckle patterns, the typical scattering patterns of CXD, by changing the samples. Finally we have successfully observed the μm/sub-μm domain arrangements in LuFe2O4/(1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3(x = 0.09), where it is hard to be observed by the conventional diffraction techniques.

DOI： 10.1080/00150193.2017.1350058

Stability of cluster glass state in nano order sized YbFe2O4 powders

H. Kobayashi, K. Fujiwara, N. Kobayashi, T. Ogawa, M. Sakai, M. Tsujimoto, O. Seri, S. Mori, N. Ikeda

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 103 103 - 108 2017年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Slow magnetic relaxation and the Fe ion stoichiometry were investigated in spin and charge frustrated system YbFe2O4. DC susceptibility, AC susceptibility, aging process and electron diffraction observation were carried out on nano order sized YbFe2O4 single-phase powders with the Fe/Yb=2.00, 2.02, and 2.04 ratios. The variation of the cluster glass behavior was studied in relation between the magnetic relaxation and the various chemical compositions. With the increase of the Fe/Yb ratios, the magnetic coherence length increased and the magnetic aging time goes slow down. The observed critical slowing down of the glassy fluctuation is interpreted by the development of the spin cluster size. This indicates that the spin glass like property of this material arises from the competition between various sized magnetic domains having ferrimagnetic moments. Additionally, electron diffraction experiments showed that the increase of Fe/Yb ratios from Fe/Yb=2.00 enhances the development of the charge ordering coherence in triangular lattice. This study shows that the measurement of magnetic fluctuation for nano order sized particles gives the essential information about the spin cluster fluctuation in RFe2O4.

DOI： 10.1016/j.jpcs.2016.12.014

Absence of a polar phase in perovskite chromite RCrO3 (R=La and Pr)

Kenji Yoshii, Naoshi Ikeda, Yutaka Shimojo, Yoshinobu Ishii

MATERIALS CHEMISTRY AND PHYSICS 190 96 - 101 2017年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE SA

Magnetic and dielectric properties have been studied for LaCrO3, PrCrO3, and their solid solution La0.5Pr0.5CrO3, which belong to a family of the ferroelectric orthochromite series RCrO3 (R: rare earths). The magnetic measurements confirm that the materials show canted antiferromagnetic ordering at 240-288 K. Neutron diffraction patterns could be fitted with the centrosymmetric Pnma, which is different from the non-centrosymmetric structure proposed for the ferroelectric phase of NdCrO3. The large dielectric constants are likely due to the hopping of charge carriers as proposed previously for other chromites. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matchemphys.2016.12.074

Crystal-Site-Selective Spectrum of Fe3O4 Obtained by Mossbauer Diffraction

Shin Nakamura, Takaya Mitsui, Kosuke Fujiwara, Naoshi Ikeda, Masayuki Kurokuzu, Susumu Shimomura

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 ( 2 ) 400 - 409 2017年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We have succeeded for the first time in obtaining a crystal-site-selective Mossbauer spectrum of Fe3O4 using the Mossbauer diffractometer at SPring-8 BL11XU. In order to extract the nuclear resonant scattering, which provides the crystal-site-selective emission spectrum, reflections having a Bragg angle near 45 degrees were used. The 666 and 10 10 0 reflection spectra reveal only B- and A-site spectra, respectively. Mossbauer diffraction spectroscopy enables us to measure the crystal-site-selective spectrum and to determine the precise hyperfine structure. This technique provides new possibilities for studying the local crystallographic and magnetic structure on iron sublattices in various multisite materials.

DOI： 10.7566/JPSJ.86.023706

Electric spontaneous polarization in YbFe2O4

T. Nagata, P. -E. Janolin, M. Fukunaga, B. Roman, K. Fujiwara, H. Kimura, J. -M. Kiat, N. Ikeda

APPLIED PHYSICS LETTERS 110 ( 5 ) 2295 - 2306 2017年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

We report the observation of the electric spontaneous polarization in YbFe2O4, one candidate "electronic ferroelectric,"where ferroelectricity originates from the polar charge order. Though we have proposed that in LuFe2O4 polar charge ordering of iron ions having different valence states give rise to ferroelectricity, some reports questioned not only the electronic origin but also the existence of the ferroelectricity itself in this system. In response to this, we show a direct macroscopic evidence of the existence of the ferroelectricity by a clear P-E hysteresis loop of YbFe2O4 belonging to the same system as that of LuFe2O4. Although further investigations are required about the electronic origin, we report the direct observation of the macroscopic electric polarization.

DOI： 10.1063/1.4974994

Possible charge order structure of stoichiometric YbFe2O4

Kosuke Fujiwara, Tomoyuki Karasudani, Mamoru Fukunaga, Hiroyuki Kobayashi, Jun Kano, Pierre-Eymeric Janolin, Jean-Michel Kiat, Yoshio Nogami, Ryusuke Kondo, Naoshi Ikeda

FERROELECTRICS 512 ( 1 ) 85 - 91 2017年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

We report a possible charge ordering model of triangular mixed valence material YbFe2O4. It was found that a crystal synthesized with high stoichiometry on iron vacancy shows new and simple extinction rule in the superlattice reflections. The Laue class of the diffraction signal is expressed as 2/m. With the consideration of the charge neutrality and the superlattice signal of (1/3 1/3 0), we derived 5 possible charge ordering models of this material.

DOI： 10.1080/00150193.2017.1349945

Ferroelectric and magnetic properties for nano particles of multiferroic YbFe2O4

Hiroyuki Kobayashi, Kosuke Fujiwara, Naoya Kobayashi, Tomoyuki Karasudani, Masahiro Sakai, Naoshi Ikeda, Shigeo Mori, Osami Seri

FERROELECTRICS 512 ( 1 ) 77 - 84 2017年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

Size effect and lattice strain effect for charge ordered structure and magnetic properties were investigated on the nano particles of geometrically spin and charge frustrated system YbFe2O4. The lattice strain of the nano particle was controlled with the ratio of Yb and Fe (2.00 Fe/Yb 2.04) in liquid synthesizing method. It was found that the lattice strain is not affected by the magnetic transition temperature, however the anomalous behavior at a lower magnetic transition (T-LT) with an increment of the Fe / Yb ratio was detected. The development of charge ordering was two-dimensional and magnetic ordering goes down for all samples in spite of the variation of the local lattice strain. This is the first report of the coupling of charge and spin ordering to the size effect in this material. These results suggest that the discussion on the electric polarization induced from the charge ordering in this material need to care the long-range interaction like surface effect.

DOI： 10.1080/00150193.2017.1349913

Development of Mössbauer diffractometer by using nuclear resonant scattering at SPring-8 BL11XU

Shin Nakamura, Takaya Mitsui, Kosuke Fujiwara, Naoshi Ikeda, Yasuhiro Kobayashi, Susumu Shimomura

Hyperfine Interact (2016) 237 2016年11月

Quantitative study of band structure in BaTiO3 particles with vacant ionic sites

Norihiro Oshime, Jun Kano, Naoshi Ikeda, Takashi Teranishi, Tatsuo Fujii, Takeji Ueda, Tomoko Ohkubo

JOURNAL OF APPLIED PHYSICS 120 ( 15 ) 2016年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

Levels of the conduction band minimum and the valence band maximum in ion-deficient BaTiO3 particles were investigated with optical band gap and ionization energy measurements. Though it is known that the quantification of the band structure in an insulator is difficult, due to the poor electrical conductivity of BaTiO3, systematic variation in the band energy levels was found that correlated with the introduction of vacancies. Photoelectron yield spectroscopy provided direct observation of the occupancy level of electrons, which is altered by the presence of oxygen and barium vacancies. In addition, the conduction band deviation from the vacuum level was determined by optical reflectance spectroscopy. Our results show that: (1) Introduction of oxygen vacancies forms a donor level below the conduction band. (2) The conduction band is shifted to a lower level by a larger number of oxygen vacancies, while the valence band also shifts to a lower level, due to the reduction in the density of O 2p orbitals. (3) Introduction of barium vacancies widens the band gap. Since barium vacancies can induce a small number of oxygen vacancies with accompanying charge compensation, this behavior suppresses any large formation of donor levels in the gap states, indicating that cation vacancies can control the number of both donor and acceptor levels. Published by AIP Publishing.

DOI： 10.1063/1.4964803

Structural, magnetic and optical properties of YbFe2O4 films deposited by spin coating

Tatsuo Fujii, Naoya Okamura, Hideki Hashimoto, Makoto Nakanishi, Jun Kano, Naoshi Ikeda

AIP ADVANCES 6 ( 8 ) 2016年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

Rare-earth iron oxides (RFe2O4) have attracting attention as new electronic device materials because of their numerous functionalities, such as electronic ferroelectricity, ferrimagnetism, and high infrared absorption. In this paper, nearly monophasic YbFe2O4 films were prepared on alpha-Al2O3 (001) substrates by the spin coating method using an aqueous-based YbFe2O4 solution. The solution was composed of a stoichiometric ratio of Yb(CH3COO)(3) and Fe(NO3)(3) with excess chelating agents. After heat treatment above 800 degrees C, well-crystallized and highly (001)-oriented YbFe2O4 started to epitaxially form on the substrate under controlled oxygen partial pressure with H-2/CO2 gas mixtures. X-ray pole figure analysis confirmed the following epitaxial relationship: YbFe2O4[100](001)//alpha-Al2O3[100](001). Moreover formation of an Fe3O4 interracial layer between YbFe2O4 and alpha-Al2O3 was detected by high-resolution transmission electron microscopy. Presence of the Fe3O4 interracial layer seemed to release the lattice misfit with the substrate. The Fe2+/Fe3+ ratio in the obtained YbFe2O4 films was nearly stoichiometric and the indirect bandgap assigned to Fe2+ -> Fe3+ charge transfer excitation was found to be similar to 0.4 eV by optical spectroscopy. A clear magnetic transition from the paramagnetic state to the ferrimagnetic state occurred at similar to 230 K. (C) 2016 Author(s).

DOI： 10.1063/1.4961639

Observation of momentum-resolved charge fluctuations proximate to the charge-order phase using resonant inelastic x-ray scattering

M. Yoshida, K. Ishii, M. Naka, S. Ishihara, I. Jarrige, K. Ikeuchi, Y. Murakami, K. Kudo, Y. Koike, T. Nagata, Y. Fukada, N. Ikeda, J. Mizuki

SCIENTIFIC REPORTS 6 2016年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

In strongly correlated electron systems, enhanced fluctuations in the proximity of the ordered states of electronic degrees of freedom often induce anomalous electronic properties such as unconventional superconductivity. While spin fluctuations in the energy-momentum space have been studied widely using inelastic neutron scattering, other degrees of freedom, i.e., charge and orbital, have hardly been explored thus far. Here, we use resonant inelastic x-ray scattering to observe charge fluctuations proximate to the charge-order phase in transition metal oxides. In the two-leg ladder of Sr14-xCaxCu24O41, charge fluctuations are enhanced at the propagation vector of the charge order (q(CO)) when the order is melted by raising temperature or by doping holes. In contrast, charge fluctuations are observed not only at q(CO) but also at other momenta in a geometrically frustrated triangular bilayer lattice of LuFe2O4. The observed charge fluctuations have a high energy (similar to 1 eV), suggesting that the Coulomb repulsion between electrons plays an important role in the formation of the charge order.

DOI： 10.1038/srep23611

Observation of all-in type tetrahedral displacements in nonmagnetic pyrochlore niobates

S. Torigoe, Y. Ishimoto, Y. Aoishi, H. Murakawa, D. Matsumura, K. Yoshii, Y. Yoneda, Y. Nishihata, K. Kodama, K. Tomiyasu, K. Ikeda, H. Nakao, Y. Nogami, N. Ikeda, T. Otomo, N. Hanasaki

PHYSICAL REVIEW B 93 ( 8 ) 2016年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We observed all-in type Nb tetrahedral displacement in nonmagnetic pyrochlore niobates A(2)Nb(2)O(7) (A = Nd0.5Ca0.5 and Y0.5Ca0.5) through the analysis of the neutron pair distribution function and the extended x-ray absorption function spectroscopy. The all-in type Nb tetrahedral displacement, which has the character of a charge singlet state, is driven by the formation of the bonding orbital. The diffuse scattering in the x-ray diffraction, which has the resonant component in the Nb L-3 edge, indicates that the all-in type Nb tetrahedral displacement has the periodicity with its short-range correlation.

DOI： 10.1103/PhysRevB.93.085109

21aPS-115 金属-強誘電体接合系における触媒作用

重名智博, 狩野旬, 池田直, 藤井達生, 大久保智子

日本物理学会講演概要集 71 2708 - 2708 2016年

21aAF-3 BaTiO_3のバンド構造におけるイオン欠損効果

押目典宏, 狩野旬, 池田直, 寺西貴志, 大崎浩司, 藤井達生, 上田剛慈, 大久保智子

日本物理学会講演概要集 71 2691 - 2691 2016年

21aPS-116 Mnをドープした(YbFe_2O_4)_m(YbFeO_3)_n, m=1, n=1単結晶の磁性と誘電特性

烏谷友之, 藤原孝将, 藤井達生, 戸取和大, 古林宏之, 福永守, 堀部陽一, 狩野旬, 池田直

日本物理学会講演概要集 71.1 2709 2016年

Control of Fermi Level by Variation of Charge Ordering State in Yb1-xTixFe2O4

Tomoko Nagata, Hiroyuki Okazaki, Takanori Wakita, Tetsushi Fukura, Nobuyuki Iwata, Hiroshi Yamamoto, Takayoshi Yokoya, Naoshi Ikeda

Transactions of the Materials Research Society of Japan 41 ( 3 ) 269 - 271 2016年

記述言語：英語出版者・発行元：一般社団法人日本MRS

<p>Fermi level and valence state were investigated in RFe₂O₄ (R = Y, Dy, Ho, Er, Tm, Yb, Lu, Sc, or In), which shows magnetoelectric effect originating from charge and magnetic orders of Fe²⁺ and Fe³⁺. We succeeded in controlling the Fermi level of YbFe₂O₄ system by Ti⁴⁺ substitution for Yb³⁺. The variation in the ratio of Fe²⁺ to Fe³⁺ is suggested to the origin of the Fermi level variation. This report suggests the possibility of simple selection of conduction type in functional oxide.</p>

DOI： 10.14723/tmrsj.41.269

Iron vacancy effect on the magnetization of YbFe2O4

K. Fujiwara, M. Miyajima, M. Fukunaga, J. Kano, H. Kobayashi, N. Ikeda

Transactions of the Materials Research Society of Japan 41 ( 1 ) 139 - 142 2016年

記述言語：英語出版者・発行元：一般社団法人日本MRS

We report the effect of iron vacancies on the magnetic property of spin and charge ordered system YbFe₂O₄ single crystals. The excess amount of iron compensates for the evaporation of iron during crystal growth. We concluded that samples grown with the standard method contain iron vacancies of more than 10%. It is considered that increasing the iron in the starting material recovers the iron stoichiometry, and the proper magnetic property appears. With recovery of the chemical stoichiometry, the magnetic hysteresis loop changes from a double loop to a single loop, which indicates the development of spin coherence and the appearance of a large ferrimagnetic domain. The anomaly found in the thermomagnetization curve at approximately 150 K, the so-called T_LT transition, disappears with better stoichiometry. This fact indicates that T_LT is not a kind of phase transition but an effect of iron vacancy. Our discovery demonstrates that most of the crystals used in RFe₂O₄ research might contain many iron vacancies. The confused discussions on this material about the spin order model, the charge order model, and so on might reconsider such chemical stoichiometry, including iron vacancies.

DOI： 10.14723/tmrsj.41.139

Pressure dependence of far-infrared reflectance spectra in layered iron oxide LuFe2O4

T. Go, H. Okamura, G. Oohata, T. Nagata, T. Moriwaki, Y. Ikemoto, S. Mori, N. Ikeda, K. Mizoguchi

Transactions of the Materials Research Society of Japan 41 ( 1 ) 109 - 112 2016年

記述言語：英語出版者・発行元：一般社団法人日本MRS

The far-infrared reflectance spectra of layered iron oxide LuFe₂O₄ have been investigated at external pressure up to 8 GPa. The observed phonon modes continuously shift to the higher energy side with increasing pressure below 6 GPa. However, it is found that the spectral profile of the phonon modes drastically changes around 6 GPa. From the analysis of the phonon modes using a Lorentz oscillator model, it is shown that the spectral changes correspond to a structural phase transition that occurs at 6 GPa.

DOI： 10.14723/tmrsj.41.109

Observation of Flux-Grown α-Fe2O3 Single Crystal at the Morin Transition by 57Fe Synchrotron Radiation Mössbauer Diffraction

Takaya Mitsui, Shin Nakamura, Naoshi Ikeda, Kosuke Fujiwara, Ryo Masuda, Yasuhiro Kobayashi, Makoto Seto

J. Phys. Soc. Jpn. 85 ( 5 ) 2016年

21pCC-5 核共鳴散乱回折装置による結晶サイト選択的メスバウアースペクトルの測定II

中村真一, 三井隆也, 藤原孝将, 池田直, 下村晋

日本物理学会講演概要集 71 1273 - 1273 2016年

層状鉄酸化物RFeMO4における短範囲秩序構造と誘電特性

吉本航, 藤原孝将, 池田直, 河口彰吾, 久保田佳基, 石井悠衣, 森茂生

日本物理学会講演概要集 71.2 2549 - 2549 2016年

記述言語：日本語出版者・発行元：一般社団法人日本物理学会

層状鉄酸化物RFe2O4は三角格子上で2価と3価のFeイオンが秩序化することにより特徴的な電荷秩序構造の形成を伴う強誘電体であり、また、低温で反強磁性転移を示すマルチフェロイック物質である。本研究では、Fe2+サイトをCo2+やCu2+等の遷移金属元素で置換することにより、特徴的な散漫散乱を与える局所構造が形成され、誘電特性等の物性に影響を与えることを見出した。また、RFe2O4型構造をもつ新しいIn系バナジウム酸化物についてもその構造と物性についても報告する予定である。

DOI： 10.11316/jpsgaiyo.71.2.0_2549

マルチフェロイック{\it R}Fe$_{2}$O$_{4}$ ({\it R}: 希土類)の元素置換効果査読

吉井賢資, 船江岳史*, 水牧仁一朗*, 江尻宏紀*, 池田直*, 齋藤寛之, 松村大樹

Physica Status Solidi (C) 12 ( 6 ) 841 - 844 2015年6月

記述言語：英語

マルチフェロイック{\it R}Fe$_{2}$O$_{4}$ ($R$: Y, Ho-Lu, In)の元素置換効果について調べた。これまでほとんど報告例のない、非磁性のGa$^{3+}$を鉄サイトに置換した場合は、磁気転移温度$T_{\rm N}$が減少した。これは過去、{\it R}FeCoO$_{4}$などでも示した通り、鉄サイト間の磁気相互作用が弱まったためである。Ga$^{3+}$置換した場合、室温の誘電率は母物質とほぼ変わらない1000-10000程度であった。また、誘電損失が減少することも判明した。この理由については現在不明であるが、損失の減少はエネルギー利用効率の上昇を示しており、応用に有利である。また$R$サイトの置換も行い、Dy$^{3+}$のような大きな$R^{3+}$を10\%程置換できることが、放射光吸収分光により判明した。なお、置換試料では$T_{\rm N}$が5-10K上昇した。この現象の起源についても現状では不明であるが、室温でマルチフェロイック状態を実現する一つの方向性を示しており、興味深い結果である。

DOI： 10.1002/pssc.201400250

Valence-specific magnetization of the charge-ordered multiferroelectric LuFe2 O4 using soft x-ray magnetic circular dichroism under 30 T pulsed high magnetic fields

Yasuo Narumi, Tetsuya Nakamura, Kota Saito, Takayuki Morioka, Yukimasa Fukada, Takashi Kambe, Naoshi Ikeda, Yoshinori Kotani, Toyohiko Kinoshita, Koichi Kindo, Hiroyuki Nojiri

Physical Review B - Condensed Matter and Materials Physics 91 ( 1 ) 2015年1月

掲載種別：研究論文（学術雑誌）

Soft x-ray magnetic circular dichroism (XMCD) have been measured on the single crystal of the charge-ordered type multiferroelectric material LuFe2O4. By comparing the XMCD results with the bulk magnetizations, the valence-specific magnetizations (VSMs) of Fe2+ and Fe3+ ions are obtained. Both Fe2+ and Fe3+ ions show positive and negative remanent VSMs below the spin ordering temperature TSO∼250 K, showing the ferrimagnetic long-range ordering directly. Both of the remanent VSMs disappear above the TSO and the field dependencies of the VSMs behave in paramagnetic fashions with convex and concave curvatures. However, the signs of the VSMs of Fe2+ and Fe3+ remain opposite, nevertheless the system is in a paramagnetic phase. This is direct evidence of the robust antiferromagnetic interaction between Fe2+ and Fe3+ ions even above the TSO. As temperature increases, furthermore, the opposite VSM of Fe3+ is reversed around the three-dimensional charge ordering temperature TCO∼330 K showing that both net magnetic moments of Fe2+ and Fe3+ become parallel to the applied magnetic field. Possible correlation between these unusual magnetic behaviors and the ferroelectric properties of LuFe2O4 is discussed.

DOI： 10.1103/PhysRevB.91.014410

Valence-specific magnetization of the charge-ordered multiferroelectric LuFe2O4 using soft x-ray magnetic circular dichroism under 30 T pulsed high magnetic fields

Yasuo Narumi, Tetsuya Nakamura, Kota Saito, Takayuki Morioka, Yukimasa Fukada, Takashi Kambe, Naoshi Ikeda, Yoshinori Kotani, Toyohiko Kinoshita, Koichi Kindo, Hiroyuki Nojiri

PHYSICAL REVIEW B 91 ( 1 ) 2015年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Soft x-ray magnetic circular dichroism (XMCD) have been measured on the single crystal of the charge-ordered type multiferroelectric material LuFe2O4. By comparing the XMCD results with the bulk magnetizations, the valence-specific magnetizations (VSMs) of Fe2+ and Fe3+ ions are obtained. Both Fe2+ and Fe3+ ions show positive and negative remanent VSMs below the spin ordering temperature T-SO similar to 250 K, showing the ferrimagnetic long-range ordering directly. Both of the remanent VSMs disappear above the TSO and the field dependencies of the VSMs behave in paramagnetic fashions with convex and concave curvatures. However, the signs of the VSMs of Fe2+ and Fe3+ remain opposite, nevertheless the system is in a paramagnetic phase. This is direct evidence of the robust antiferromagnetic interaction between Fe2+ and Fe3+ ions even above the T-SO. As temperature increases, furthermore, the opposite VSM of Fe3+ is reversed around the three-dimensional charge ordering temperature T-CO similar to 330 K showing that both net magnetic moments of Fe2+ and Fe3+ become parallel to the applied magnetic field. Possible correlation between these unusual magnetic behaviors and the ferroelectric properties of LuFe2O4 is discussed.

DOI： 10.1103/PhysRevB.91.014410

10 fs Dynamics of Photoinduced Magnetic Transition in Double-Layered Charge Ordering in LuFe2O4 Under Interlayer Excitation 査読

Y. Sagae, K. Yamada, T. Ishikawa, K. Itoh, H. Itoh, T. Sasaki, T. Nagata, J. Kano, T. Kambe, S. Ishihara, N. Ikeda, S. Iwai

Springer Proceedings in Physics 162 (Ultrafast Phenomena XIX) 252 - 256 2015年1月

Mössbauer Spectroscopy of Novel Ferroelectric Materials

Shin Nakamura, Jun Kano, Norihiro Oshime, Naoshi Ikeda, Yasuhiro Kobayashi, Shinji Kitao, Makoto Seto

KURRI Progress Report 2014 78 2015年

Elemental substitution effects in multiferroic RFe2O4 (R: rare earths)

Kenji Yoshii, Takashi Funae, Masaichiro Mizumaki, Hiroki Ejiri, Naoshi Ikeda, Hiroyuki Saitoh, Daiju Matsumura

PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 12, NO 6 12 ( 6 ) 841 - 844 2015年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：WILEY-V C H VERLAG GMBH

We report the effects of elemental substitutions in multiferroic RFe2O4 (R: Y, Ho-Lu, In). The substitution by nonmagnetic Ga3+ at the Fe site, which has not been reported so far, shows a drastic decrease in the ferrimagnetic transition temperature (TN). This is plausibly owing to the suppression of magnetic interactions between Fe ions, based on our previous results of other substituted systems such as RFeCoO4. Dielectric constants near room temperature were comparable to those of RFe2O4. The suppression of dielectric loss in this system is suitable to application. The R-site substitution was also attempted by the large R3+ ions such as Dy3+. The solubility limit was up to similar to 10% of R ions. TN was raised by 5-10 K for Dy3+ substitution. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.201400250

16aAD-4 複鉄酸化物YbFe_2O_4のFe 3p-3d共鳴光電子分光

福良哲司, 脇田高徳, 竹田彩, 寺嶋健成, 藤原孝将, 池田直, 村岡祐治, 横谷尚睦

日本物理学会講演概要集 70 2405 - 2405 2015年

17aCH-1 核共鳴散乱回折装置による結晶サイト選択的メスバウアースペクトルの測定

中村真一, 三井隆也, 池田直, 藤原孝将, 小林康浩

日本物理学会講演概要集 70 865 - 865 2015年

18aAD-9 核ブラッグモノクロメーターによる放射光メスバウアーγ線回折の研究

三井隆也, 中村真一, 池田直, 藤原孝将, 小林康浩

日本物理学会講演概要集 70 2489 - 2489 2015年

18aPS-73 BaTiO_3に接合した金属微粒子の価数異常

吉田右, 狩野旬, 押目典宏, 日隈聡士, 加藤和男, 新田清文, 水牧仁一朗, 池田直, 藤井達生, 大久保智子, 上田剛慈

日本物理学会講演概要集 70 2505 - 2505 2015年

Temperature and polarization dependence of Fe L-3-edge X-ray absorption spectra of LuFe2O4

A. Agui, M. Mizumaki, T. Kuroda, M. Kawai, T. Nagata, N. Ikeda, T. Uozumi

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 197 13 - 16 2014年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The charge ordering of Fe2+ and Fe3+ ions in LuFe2O4 induces ferroelectricity below 330 K. In this study, the X-ray absorption spectra (XAS) at the Fe L-2,L-3-edge are investigated to study charge ordered- and disordered-states. The polarization dependence of XAS revealed that the energy level of (d(xy), d(x2-y2)) is lower than that of (d(yz), d(zx)). In the charge-ordered state, the Fe L-3-XAS shows a double-peak structure, which is a characteristic of Fe2+ and Fe3+ ions. In the high-temperature region, the double-peak structure becomes a broad single peak, because of overlap with the thermally excited state. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2014.08.008

Current-Induced Enhancement of Magnetic Anisotropy in Spin-Charge-Coupled Multiferroic YbFe2O4

Kenji Yoshii, Daiju Matsumura, Hiroyuki Saitoh, Takashi Kambe, Mamoru Fukunaga, Yuji Muraoka, Naoshi Ikeda, Shigeo Mori

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 83 ( 6 ) 2014年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We report the change in the magnetic properties of multiferroic YbFe2O4 caused by cooling in the presence of an electrical current. The magnetization measured after the cooling is similar to 10-20% smaller than that after cooling without a current. The current also affects the magnetic anisotropy below similar to 100 K; the magnetic coercivity is increased by similar to 10-20%. These phenomena may arise from the coexistence of ferromagnetic and antiferromagnetic domains or a disturbance in the formation of charge-ordered domains. From the viewpoint of application, the enhancement of anisotropy by an electrical current provides a method for stabilizing magnetization other than the well-known method of exchange bias.

DOI： 10.7566/JPSJ.83.063708

Valence instability of iron oxide ultrafine particles on ferroelectrics studied by Mossbauer spectroscopy

Jun Kano, Takumi Okamoto, Shin Nakamura, Akio Fuwa, Takafumi Otoyama, Yoshiaki Nakazaki, Hideki Hashimoto, Jun Takada, Norihiro Oshime, Miho Ito, Naoshi Ikeda

JAPANESE JOURNAL OF APPLIED PHYSICS 53 ( 5 ) 2014年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP PUBLISHING LTD

Various types of iron oxides loaded on ferroelectric BaTiO3 and nonferroelectric ZrO2 supports have been studied by Fe-57 Mossbauer spectroscopy to investigate the valence instability of iron oxides affected by ferroelectric polarization fluctuation. Although the iron oxide loaded on ZrO2 shows a typical reduction process at high vacuum and high temperature, the iron oxide loaded on BaTiO3 shows an opposite process, i.e., iron oxide oxidization. We propose the dynamics of band structures of ferroelectrics in the paraelectric phase to understand this phenomenon. The oscillation of band bending causes electron transfer from an iron oxide to a ferroelectric support. This result suggests that the surface charges of ferroelectrics are useful in developing new functional materials with metal compounds. (C) 2014 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.53.05FB24

Specific Heat Study of Multiferroic LuFe2O4 Single Crystal

N. Hasegawa, T. Mitsumura, M. Takesada, A. Onodera, J. Kano, N. Ikeda

FERROELECTRICS 462 ( 1 ) 145 - 150 2014年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

Precise measurements of specific heat were performed on high quality single crystals of multiferroic LuFe2O4 by using an ac calorimeter. The thermal anomalies corresponding to four known phase transitions were observed at 220K (T-g), 260K (T-N), 380K (T-3CO) and 590K (T-2CO). In addition to them, a new clear anomaly was detected at 305K. No other distinct anomaly could be observed below 220K down to 100K. It is clarified that the temperature dependence of the order parameter associated with this new phase transition at 305K is quite similar to those of spontaneous polarization reported previously by Ikeda etal.

DOI： 10.1080/00150193.2014.890505

Preparation and electronic properties YbFe2O4 thin films by polymerized complex method

N. Okamura, T. Fujii, J. Takada, M. Nakanishi, J. Kano, N. Ikeda

Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy 61 S327 - S329 2014年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Japan Society of Powder and Powder Metallurgy

Rare-earth iron oxides (RFe2O4) have attracting attention as new electronic device materials because of their abundant functionalities such as ferroelectricity, ferrimagnetism, and high infrared absorption. These properties are strongly related to the mixed iron valance states between Fe2+ and Fe3+. We tried to prepare RFe2O4 films by using soft chemical method. The films were prepared by spin-coating of viscous aqueous solutions of Yb(CH3COO)3 and Fe(NO3)3 with citric acid. The molar ratio between Yb:Fe was 1:2 and the citric acid: metal ratio was set to 3.75:1. After the coating, the films dried at 100ï¿½C for 10 min in air were, heat-treated at 900ï¿½C for 0.2 h in H2/CO2 gases to control oxygen partial pressure, and quenched. The obtained films were characterized by using XRD, SEM, EDS, Mï¿½ssbauer, and optical-absorption spectra. The XRD pattern clearly indicated the well-crystallized and nearly monophasic YbFe2O4 formed on the substrates above 900ï¿½C to control the oxygen partial pressure. Equal amount of Fe2+ and Fe3+ ions was present in the films. The films showed small band-gap and large optical absorbance in infrared region.

DOI： 10.2497/jjspm.61.S327

Carrier mobility of iron oxide nanoparticles supported on ferroelectrics studied by Mössbauer Spectroscopy

Takumi Okamoto, Jun Kano, Shin Nakamura, Akio Fuwa, T. Otoyama, Y. Nakazaki, Hideki Hashimoto, J. Takada, Miho Ito, Naoshi Ikeda

Hyperfine Interactions 219 ( 1-3 ) 147 - 152 2013年4月

Magnetoelectric Effect Driven by Magnetic Domain Modification in LuFe2O4

Takashi Kambe, Yukimasa Fukada, Jun Kano, Tomoko Nagata, Hiroyuki Okazaki, Takayoshi Yokoya, Shuichi Wakimoto, Kazuhisa Kakurai, Naoshi Ikeda

PHYSICAL REVIEW LETTERS 110 ( 11 ) 117602 2013年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The magnetocapacitance effect was investigated using impedance spectroscopy on single crystals of LuFe2O4. The intrinsic impedance response could be separated from the interfacial response and showed a clear hysteresis loop below T-Ferri similar to 240 K under the magnetic field. The neutron diffraction experiment under the magnetic field proves the origin of the dielectric property related to the motion of the nanosized ferromagnetic domain boundary. These results imply that the modification of the microscopic domain structure is responsible for the magnetoelectric effect in LuFe2O4. DOI: 10.1103/PhysRevLett.110.117602

DOI： 10.1103/PhysRevLett.110.117602

Magnetic properties of single crystalline YbFe2O4

K. Yoshii, M. Mizumaki, K. Matsumoto, S. Mori, N. Endo, H. Saitoh, D. Matsumura, T. Kambe, N. Ikeda

XXIST INTERNATIONAL SYMPOSIUM ON THE JAHN-TELLER EFFECT 2012 428 012032 2013年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

We have investigated the magnetic properties of a single crystal of multiferroic YbFe2O4. Ferrimagnetic ordering of Fe spins is observed at similar to 250 K. The magnetization measured during field cooling becomes negative below similar to 10 K owing to the antiparallel coupling between the Fe and Yb sublattices. The magnetization below similar to 10 K is flipped by changing the applied magnetic field in a positive direction, a property which may be used to the development of magnetic devices. Magnetocaloric measurements show a broad peak of the entropy change, likely owing to a multiple magnetic transition.

DOI： 10.1088/1742-6596/428/1/012032

Nonlinear Electric Conductivity of Charge Ordered System RFe2O4 (R = Lu, Yb)

T. Nagata, Y. Fukada, M. Kawai, J. Kano, T. Kambe, E. Dudzik, R. Feyerherm, P. E. Janolin, J. M. Kiat, N. Ikeda

FERROELECTRICS 442 ( 1 ) 45 - 49 2013年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

We report nonlinear conductivity associated with a phase transition in polar charge ordered material YbFe2O4. To investigate the existence of nonlinear conductivity, we measured temperature dependence of conductivity as a function of applied electric current and estimated the sample heating precisely. Then we found the nonlinear conductivity below three dimensional charge ordering temperature 340 K. The result is consistent with diffraction observation.

DOI： 10.1080/00150193.2013.773874

Magnetic properties of R2Fe3O7 (R=Yb and Lu)

K. Yoshii, N. Ikeda, R. Fukuyama, T. Nagata, T. Kambe, Y. Yoneda, T. Fukuda, S. Mori

Solid State Communications 173 34 - 37 2013年

記述言語：英語掲載種別：研究論文（学術雑誌）

We have investigated the magnetic properties of R2Fe 3O7 (R=Yb and Lu), which belongs to the homologous family of electronic ferroelectric RFe2O4. Magnetization measurements show ferrimagnetic ordering at the Néel temperature (T N) of ∼270 K, which is slightly higher than that of RFe 2O4 (TN∼230-250 K). Observation of spin glass and exchange bias shows a coexistence of ferromagnetic and antiferromagnetic interactions, similarly to RFe2O4. This situation gives rise to a complex magnetic change and a broad peak of magnetic entropy change. Some characteristics, such as refrigeration temperatures higher than in RFe2O4, seem to offer a possibility of this system to applications. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2013.08.030

Exchange Bias in Multiferroic RFe2O4 (R = Y, Er, Tm, Yb, Lu, and In)

Kenji Yoshii, Naoshi Ikeda, Yasuo Nishihata, Daisuke Maeda, Ryota Fukuyama, Tomoko Nagata, Jun Kano, Takashi Kambe, Yoichi Horibe, Shigeo Mori

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 ( 3 ) 33704 2012年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

An exchange bias (EB) behavior has been observed for multiferroic RFe2O4 (R Y, Er, Tm, Yb, Lu, and In). The materials with small R3+ ions (R = Tm, Yb, Lu, and In) exhibit large EB fields (greater than or similar to 1 kOe) below similar to 100-150 K. This property is rooted in a magnetically glassy state, arising from the competition between ferromagnetic and antiferromagnetic domain interactions. In addition, the EB field tends to be more enhanced for smaller R3+ ions. Hence, the EB is controlled by the substitution at the R-site in this series.

DOI： 10.1143/JPSJ.81.033704

Ferroelectricity and Ferrimagnetism of Hexagonal YbFeO3 Thin Films

Hayato Iida, Takuro Koizumi, Yoshiaki Uesu, Kay Kohn, Naoshi Ikeda, Shigeo Mori, Raphael Haumont, Pierre-Eumeric Janolin, Jean-Michel Kiat, Mamoru Fukunaga, Yukio Noda

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 ( 2 ) 24719 2012年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

The coexistence of ferroelectricity and magnetic order in epitaxial hexagonal YbFeO3 (h-YbFeO3) thin films deposited on yttria stabilized zirconia substrates is examined using an impedance analyzer, a second harmonic generation (SHG) microscope, an X-ray diffractometer, a transmission electron microscope and a superconducting quantum interference device magnetometer. The results show that h-YbFeO3 films exhibit ferroelectricity below 350K with threefold translational periodicity along the [110] direction similar to rare earth manganese oxides, and ferrimagnetism with a four-up and two-down spin configuration of Fe+3 and Yb+3 ions along the c-axis at low temperatures. In addition, a possibility of new ferroelectric phases with an electronic origin induced by the magnetic ordering is discussed based upon SHG and D-E hysteresis measurements.

DOI： 10.1143/JPSJ.81.024719

Magnetic and dielectric study of Bi2CuO4

K. Yoshii, T. Fukuda, H. Akahama, J. Kano, T. Kambe, N. Ikeda

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 471 ( 21-22 ) 766 - 769 2011年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Magnetic and dielectric properties have been investigated for Bi2CuO4, which has the same chemical formula as that of the parent materials of cuprate superconductors R2CuO4 (R: rare earths). Magnetization measurements show the antiferromagnetic transition of the Cu2+ spins at similar to 42 K, as reported previously. Dielectric measurements for the frequencies of 1 kHz to 1 MHz show that the dielectric constants are 100-500 at room temperature. The dielectric dispersion reveals that the dielectric response lacks spatial coherence, a property which indicates the possible existence of phase separation as suggested for La2CuO4. The imaginary part of dielectric response gives the activation energy of 0.22 eV, suggesting that the dielectric response is governed by the electron hopping between the Cu ions. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2011.05.049

電荷及びスピンフラストレーション系YbFe$_{2}$O$_{4}$における電荷秩序崩壊過程査読

松本圭右*, 小山司*, 森茂生*, 吉井賢資, 池田直*

Journal of Physics; Conference Series 320 012085\_1 - 012085\_5 2011年9月

記述言語：英語

表記酸化物はFe$^{3+}$とFe$^{2+}$が電荷秩序配列することによる新規なタイプの強誘電体である。本物質につき、Feの一部をMnに置き換えた場合の電荷秩序構造の変化を透過電子顕微鏡により観察した。10\%ほどの置換により、電荷秩序構造は破壊され、Fe$^{3+}$とMn$^{2+}$の短距離イオン秩序が発生することがわかった。この系は室温で比誘電率が1000ほどの値を示すが、この性質は短距離イオン秩序による電気双極子を起源とすると考えられる。

DOI： 10.1088/1742-6596/320/1/012085

Electronic phase transition of the valence-fluctuating fulleride Eu2.75C60

Yusuke Yamanari, Yuta Suzuki, Kumiko Imai, Eiji Shikoh, Akihiko Fujiwara, Naoko Kawasaki, Naoshi Ikeda, Yoshihiro Kubozono, Takashi Kambe

PHYSICAL REVIEW B 83 ( 24 ) 2011年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The electronic properties of Eu2.75C60 are studied using magnetic susceptibility and electron spin resonance (ESR) from 2 to 300 K. Both the magnetic susceptibility and the ESR parameters clearly show an anomaly around the valence transition temperature, T-V = 70 K. The magnetic susceptibility shows weak temperature dependence above T-V, while it changes drastically to Curie-Weiss behavior below T-V. The low-temperature susceptibility can be reproduced by assuming the moment of free Eu2+ ions. This result reveals that Eu2.75C60 changes from the intermediate valence state to the divalent state below T-V. Although ESR signals above T-V should be attributed to conduction electrons, the ESR intensity below T-V follows the Curie-Weiss law with a distinct increase in the g-factor. This should be associated with a strong localization of pi electrons. We also found that, below similar to 17 K, the isothermal magnetization exhibits a weak hysteresis and thermoremanent magnetization appears. These results suggest that valence-ordered Eu2.75C60 undergoes antiferromagnetic ordering with a weak ferromagnetic component at the Neel temperature, T-N = 17 K.

DOI： 10.1103/PhysRevB.83.245103

Multiferroic Character and Magnetic Phase of LuFe2O4

Daisuke Ohishi, Hironori Hayakawa, Hiroshi Akahama, Naoshi Ikeda, Takashi Kambe, Yoji Matsuo, Noboru Kimizuka, Jun Kano, Kenji Yoshii

FERROELECTRICS 415 51 - 56 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

The variation of AC dielectric constant in the function of the DC magnetic fields was found in low oxygen vacant LuFe2O4 single crystal in which the electric polarization arise from the polar charge ordering. These magneto-electric coupling should be explained by a novel mechanism where the boundary motion of the polar charge ordered domain is affected by the magnetic (spin) domain boundary motion.

DOI： 10.1080/00150193.2011.577371

Doping effect on charge ordered structure in Mn-doped YbFe2O4

K. Matsumoto, T. Koyama, S. Mori, K. Yoshii, T. Kambe, N. Ikeda

3RD INTERNATIONAL CONGRESS ON CERAMICS (ICC3): ADVANCES IN ELECTRO CERAMICS 18 2011年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

Changes of charge ordered (CO) structure by partial substitution of Mn for Fe in YbFe2O4 were investigated by a transmission electron microscope (TEM), in combination with conventional dielectric measurement. It is revealed that partial substitution of Mn2+ for Fe2+ in YbFe2O4 destroyed drastically the CO structure with the wave vector of q=<1/3 1/3 1/2>. Consequently polar clustering structure giving rise to honeycomb-shaped diffuse streaks was found in YbFeMnO4. The random distribution of polar clustering structure gives rise to characteristic broad dielectric dispersion.

DOI： 10.1088/1757-899X/18/9/092047

Ultrafast melting of charge ordering in LuFe2O4 probed by terahertz spectroscopy

H. Itoh, K. Itoh, K. Anjyo, H. Nakaya, H. Akahama, D. Ohishi, S. Saito, T. Kambe, S. Ishihara, N. Ikeda, S. Iwai

Journal of Luminescence 2011年

Terahertz Spectroscopy of Electronic Ferroelectric LuFe2O4 Crystal 査読

Kitahara Hideaki, Kano Jun, Fukada Yukimasa, Kambe Takashi, Ikeda Naoshi, Hangyo Masanori

2011 36TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES (IRMMW-THZ) 2011年

Direct observation of low-temperature superstructure in spin- and charge-frustrated ferrite YFe<inf>2</inf> O<inf>4-δ</inf>

Y. Horibe, N. Ikeda, K. Yoshii, S. Mori

Physical Review B - Condensed Matter and Materials Physics 82 2010年11月

The low-temperature superstructure of YFe2 O4-δ was carefully investigated by transmission electron microscopy. We found that the unique superstructure at about 100 K is characterized by 1̄ /142/71/14 -type superlattice reflection spots, suggesting the presence of charge-reordering process. The low-temperature high-resolution images clearly show superlattice modulations in Y-O layers as well as Fe-O layers. The modification of intrabilayer charge interactions due to lattice distortions in Y-O layers is discussed to play a crucial role in the stabilization of long-periodic superstructures at low temperatures. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevB.82.184119

Magnetic and dielectric study of R0.5Sr0.5MnO3 (R = Gd, Tb and Dy)

Kenji Yoshii, Yusuke Hiramitsu, Yuka Okajima, Yasuhiro Yoneda, Yasuo Nishihata, Jun'ichiro Mizuki, Akio Nakamura, Yutaka Shimojo, Yoshinobu Ishii, Yukio Morii, Naoshi Ikeda

MATERIALS RESEARCH BULLETIN 45 ( 11 ) 1574 - 1580 2010年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Magnetic and dielectric properties of perovskite manganites R0.5Sr0.5MnO3(R = Gd, Tb and Dy) have been investigated. DC and AC magnetic measurements showed short-range glassy magnetic ordering at T-g similar to 40 K. Such ordering was observed by neutron diffraction and is ascribable to the size mismatch of R3+ and Sr3+ settled randomly at the same crystallographic site. Dielectric constants for each material were similar to 1000-10,000 between similar to 50 and similar to 300 K and showed broad maximums above T-g. Dielectric dispersion showed poor coherency of the motion of polar regions, plausibly because of the size-mismatch effect; both the magnetic and dielectric properties of this system are governed by the randomness at the R/Sr site. The tan delta and EXAFS data suggest that the dielectric response is rooted in a transfer of the Mn-3d electrons. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.materresbull.2010.07.024

Quantitative analysis of O-2 gas sensing characteristics of picene thin film field-effect transistors

Xuesong Lee, Yasuyuki Sugawara, Akio Ito, Shuhei Oikawa, Naoko Kawasaki, Yumiko Kaji, Ryoji Mitsuhashi, Hideki Okamoto, Akihiko Fujiwara, Kenji Omote, Takashi Kambe, Naoshi Ikeda, Yoshihiro Kubozono

ORGANIC ELECTRONICS 11 ( 8 ) 1394 - 1398 2010年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

O-2 gas sensing behaviors are studied in picene thin film field-effect transistors (FETs) with hydrophobic polymer (Cytop(TM) or polystyrene) coated SiO2 gate dielectrics. Picene thin film FETs show a rapid reduction of hysteresis in transfer curves recorded in forward and reverse measurement modes, compared to a picene FET with hexamethydisilazane-coated SiO2. The picene FETs show very sensitive O-2 gas sensing effects down to similar to 10 ppm. A quantitative analysis is presented of the gate voltage (V-G) dependent mobility induced by O-2 exposure, i.e., the suppression of drain current at high V-G. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2010.06.003

Relaxation of geometrical frustration in NbSe3 topological crystals

T. Tsuneta, K. Yamamoto, N. Ikeda, Y. Nogami, T. Matsuura, S. Tanda

PHYSICAL REVIEW B 82 ( 1 ) 014105 2010年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Here we report the structural study of NbSe3 topological crystals via synchrotron x-ray measurements on individual microcrystals. Topological crystals are characterized by the shape of a ring or a twisted loop, thereby representing a translational and orientational order confined in topologically nontrivial, curved geometries. The crystal lattice of topological crystals is under considerable amount of strain. The volume-averaged strain asymptotically increases with thickness and curvature of a crystal. We present a structural model in which a ring crystal is composed of well-ordered domains in the shape of concentric cylinders. The internal structure reflects periodic accumulation and release of strain during the growth.

DOI： 10.1103/PhysRevB.82.014105

Charge Order Competition Leading to Nonlinearity in Organic Thyristor Family

Yoshio Nogami, Noriaki Hanasaki, Masashi Watanabe, Kenichiro Yamamoto, Takayoshi Ito, Naoshi Ikeda, Hiroyuki Ohsumi, Hidenori Toyokawa, Yukio Noda, Ichiro Terasaki, Hatsumi Mori, Takehiko Mori

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 ( 4 ) 44606 2010年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Simultaneous synchrotron radiation and transport measurements for the organic thyristor family compound theta-(BEDT-TTF)(2)RbZn(SCN)(4) have revealed the presence of microscopic competing domains between the twofold and 3 x 4 charge orderings in a triangular lattice. In contrast to conventional correlated electron systems, charge ordering is a unique critical parameter of phase competition. With external current, only the twofold ordering melts, which is responsible for the emergence of a nonlinear response.

DOI： 10.1143/JPSJ.79.044606

Growth and characterization of bismuth magnesium titanate Bi(Mg 1/2Ti1/2)O3

Yasuhiro Yoneda, Hiroyuki Saitoh, Kenji Yoshii, Takashi Nishida, Hironori Hayakawa, Naoshi Ikeda

Key Engineering Materials 421-422 3 - 8 2010年2月

A new oxide, Bi(Mg1/2Ti1/2)O3 was prepared using a high-pressure high-temperature technique at 8 GPa and 1000°C. As-sintered Bi(Mg1/2Ti1/2)O3 has the BiFeO 3-type perovskite structure with the rhombohedral R3c. After ground, crystal structure changed to tetragonal P4mm. Structure parameters of tetragonal Bi(Mg1/2Ti1/2)O3 were refined from laboratory X-ray powder diffraction data (a = 4.033(10) Å, and c = 3.938(10) Å). Bi(Mg1/2Ti1/2)O3 does not decompress at ambient pressure, but the structure changed from rhombohedral to tetragonal on heating above 800° C. This phase transition was nonreversible. Bi(Mg 1/2Ti1/2)O3 is expected to be one of the end members of lead-free ferroelectric materials. © (2010) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/KEM.421-422.30

Doping effect on charge ordered structure in RFe<inf>2</inf>O<inf>4</inf> (R=Lu and Yb)

Y. Matsuo, S. Mori, A. Hirata, K. Yoshii, N. Ikeda

Journal of Physics: Conference Series 200 2010年1月

Doping effects on the charge ordered (CO) structure in RFe 2O4 (R=Lu, Yb) were investigated by an energy-filtered transmission electron microscope (EF-TEM), in combination with conventional magnetic measurement. The repalcement of Cu2+ and Co2+ for Fe2+ in RFe2O4 (R=Lu, Yb) destroyed drastically the CO structure. In LuFeCuO4, the CO structure with q=1/3 1/3 1/2 disappear and short-ranged domains consisting of cationic ordering of Fe3+ and Cu2+ ions are formed, which gives rise to characteristic zigzag-shaped diffuse streaks with diffuse spots at the h/3-δ h/3-δ 0-type positions (h: integer, δ=0.06) in reciprocal space. In addition, the magnetic measurement revealed that LuFeCuO4 exhibits a magnetic transition around 50K, which is much lower than the Neel temperature of 250K in LuFe2O4. In YbFeCoO4, clusters consisting of Fe3+ and Co2+ in the triangular lattice are formed and give rise to honeycomb-shaped diffuse streaks. © 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/200/1/012128

Multi-ferroicity of thin-film-stabilized hexagonal YbFeO<inf>3</inf>

Y. Uesu, H. Iida, T. Koizumi, K. Kohn, S. Mori, N. Ikeda, R. Haumont, J. M. Kiat

Proceedings of the 2010 IEEE International Symposium on the Applications of Ferroelectrics, ISAF 2010, Co-located with the 10th European Conference on the Applications of Polar Dielectrics, ECAPD 2010 2010年1月

The modulated structure and ferromagnetic insulating state in a nine-layer BaRuO3

Chao-Hung Du, Chang-Hung Yao, Dah-Chin Ling, Mau-Tsu Tang, Fon-Chi Hsu, Hsiang-Lin Liu, P. D. Hatton, Naoshi Ikeda

JOURNAL OF PHYSICS-CONDENSED MATTER 22 ( 3 ) 3036003 2010年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP PUBLISHING LTD

We report the observation of a modulated structure and a ferromagnetic insulating state in a high quality single crystal of a nine-layer BaRuO3. Using x-ray scattering, the modulated satellites were observed to double the unit cell along the c-axis at low temperature. The ferromagnetic insulating state is confirmed by magnetic and resistivity measurements. Analyzing the peak profiles from the modulation and host structure respectively, showed a lattice distortion at T similar to 55 K. These findings elucidate the intimate relationship between ferromagnetism and lattice distortion in a nine-layer BaRuO3.

DOI： 10.1088/0953-8984/22/3/036003

Magneto-electric effect in charge-ordered LuFe2O4

Takashi Kambe, Takuma Komatsu, Takamasa Michiuchi, Hiroki Hayakawa, Daisuke Ohishi, Noriaki Hanasaki, Kenji Yoshii, Naoshi Ikeda

INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 012077 2010年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

A magneto-electric (ME) effect was observed in a charge-ordered ferroelectric LuFe2O4. The dielectric response in a three-dimensional charge-ordered phase is strongly influenced by magnetic field, especially around the fern-magnetic ordering temperature. We also show the relation between the oxygen stoichiometry and the ME signal character above the magnetic transition temperature.

DOI： 10.1088/1742-6596/200/1/012077

High Pressure and Temperature Synthesis of Bi-based Perovskite (Bi0.5Na0.5-xLix)TiO3

Masanori Fukunaga, Yasuhiro Yoneda, Ryota Fukuyama, Hiroyuki Saitoh, Naoshi Ikeda, Yoshinori Katayama

Transactions of the Materials Research Society of Japan 35 ( 1 ) 111 - 114 2010年

Structural characterization and dielectric properties of hexagonal Lu(Fe, Ti)O<inf>3</inf>

Yoji Matsuo, Takuya Hoshiyama, Shigeo Mori, Kenji Yoshii, Yuichi Michiue, Takashi Kambe, Naoshi Ikeda, Francisco Brown, Noboru Kimizuka

Japanese Journal of Applied Physics 48 ( 9 ) 09KB04 - 09KB04-3 2009年12月

記述言語：英語出版者・発行元：Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physics

We investigated the average crystal structure and microstructures of LuFe0.56Ti0.44O3 by transmission electron microscopy (TEM) in combination with dielectric measurements. In this work, high-quality polycrystalline samples of LuFeM0.56Ti 0.44O3 were successfully synthesized in air by the conventional solid-state reaction. The average crystal structure at room temperature is characterized by a hexagonal structure (space group: P6 3cm). Dielectric measurements revealed that LuFe 0.56Ti0.44O3 shows broad dielectric peaks at approximately 450 and 580K, one of which is considered to originate from the formation of polar domains at the nanometer scale. © 2009 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.48.09KB04

Oxygen-deficient effect on charge ordering in spin- and charge-frustrated ferrite YFe2O4−δ

Y. Horibe, K, N. Ikeda, S. Mori

Phys. Rev. B 80 ( 9 ) 092104-092104 2009年9月

Syntheses, Structures and Solid-State Properties of MMX Mixed-Valence Chains, [Ni-2(II/III)(RCS2)(4)I](infinity) (R = Et, n-Pr and n-Bu): Evidence of a Spin-Peierls Transition

Minoru Mitsumi, Yuji Yoshida, Akihisa Kohyama, Yasutaka Kitagawa, Yoshiki Ozawa, Mototada Kobayashi, Koshiro Toriumi, Makoto Tadokoro, Naoshi Ikeda, Mitsutaka Okumura, Mohamedally Kurmoo

INORGANIC CHEMISTRY 48 ( 14 ) 6680 - 6691 2009年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

The partial oxidation of [Ni-2(II/II)(RCS2)(4)] (R = Et (1), n-Pr (2), and n-Bu (3)) with iodine affords the MMX chain compounds [Ni-2(II/III)(RCS2)(4)I](infinity) (R = Et (4), n-Pr (5), and n-Bu (6)), respectively. The crystal structures of 4-6 consist of neutral one-dimensional (1-D) chains with a repeating -Ni-Ni-I- unit. The room-temperature (RT) structure of 4 indicates a charge-polarization (CP) state {-Ni(2.5-delta)+-Ni(2.5+delta)+I--Ni(2.5-delta)+ -Ni(2.5+delta)+-I- (delta << 0.5)} close to an averaged valence state judged by the Ni-I distances. In contrast, 5 and 6 exhibit a Vold periodicity of a -Ni-Ni-l- unit due to the disorder of the dithiocarboxylato ligands. Compounds 4-6 show typical semiconducting behavior and exhibit an intense sharp absorption band centered at 5400 cm(-1), which is attributed to a Mott-Hubbard gap due to a relatively large on-site Coulomb repulsion energy U of the nickel atoms. The high-temperature magnetic susceptibilities of 4-6 can be described by a 1-D Heisenberg antiferromagnetic chain model with vertical bar J vertical bar/k(B) ranging from 898(2) to 939(3) K. Compounds 4 and 5 undergo a spin-Peierls (SP) transition at relatively high T-sp = 47 and 36 K, respectively, which are accompanied by superlattice reflections corresponding to a 2-fold -Ni-Ni-l- period below T-sp. By determining the superstructure of 4 at 26 K, we conclude that the valence-ordered state changes from the CP in the RT phase to the altemate charge-polarization (ACP) state of -Ni(2.5-delta)+-Ni(2.5+delta)+-I--Ni(2.5-delta)+-I-Ni(2.5+delta)+-Ni(2.5-delta)+-I- -in the SP phase. Such a spin-Peierls transition could not be observed for 6.

DOI： 10.1021/ic900630a

Magnetic and dielectric properties of YbFe2-xMnxO4 (0 <= x <= 1)

Kenji Yoshii, Naoshi Ikeda, Takamasa Michiuchi, Yusuke Yokota, Yuka Okajima, Yasuhiro Yoneda, Yoji Matsuo, Yoichi Horibe, Shigeo Mori

JOURNAL OF SOLID STATE CHEMISTRY 182 ( 7 ) 1611 - 1618 2009年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE

We have investigated the magnetic and dielectric properties of YbFe2-xMnxO4 (0 <= x <= 1), which is all Fe-site-substituted system of new multiferroic oxides RFe2O4 (R = Y, Ho-LU). X-ray diffraction measurements show that a solid solution is formed between YbFe2O4 (x = 0) and YbFeMnO4 (X = 1) for (0 <= x <= 1), whereas only compounds with x = 1 (i.e., RM1M2O4: M-1 and M-2 = trivalent and divalent cations, respectively) have been known for the Fe-site substitution in RFe2O4. The valence of the Mn ion is determined to be similar to 2+, consistently with the Suppression of low-temperature magnetization by the Mn substitution. The magnetic transition temperature (T-N) and the dielectric constant (epsilon') decrease monotonically with increasing x. This result plausibly confirms that the magnetic and dielectric properties in oxides isostructural with RFe2O4 are governed by the electron transfer between Fe-site ions, Unlike ordinary ferroelectrics and dielectrics, in which the ionic displacement plays a key role. The possibility for application is briefly discussed as well. (C) 2009 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jssc.2009.04.008

High-performance C-60 and picene thin film field-effect transistors with conducting polymer electrodes in bottom contact structure

Yumiko Kaji, Ryoji Mitsuhashi, Xuesong Lee, Hideki Okamoto, Takashi Kambe, Naoshi Ikeda, Akihiko Fujiwara, Minoru Yamaji, Kenji Omote, Yoshihiro Kubozono

ORGANIC ELECTRONICS 10 ( 3 ) 432 - 436 2009年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

C-60 and picene thin film field-effect transistors (FETs) in bottom contact structure have been fabricated with poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PED-OT:PSS) electrodes for a realization of mechanical flexible organic FETs. The C-60 thin film FETs showed n-channel enhancement-type characteristics with the field-effect mobility mu value of 0.41 cm(2\) V-1 s(-1), while the picene thin film FET showed p-channel enhancement-type characteristics with the p of 0.61 cm(2) V-1 s(-1). The p values recorded for C-60 and picene thin film FETs are comparable to those for C-60 and picene thin film FETs with Au electrodes. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2009.01.006

希土類-鉄酸化物RFe_2O_4の示す新規な強誘電性(R = Y, Ho-Lu)

吉井賢資, 池田直, 松尾祥史, 森茂生

日本結晶学会誌 51 ( 2 ) 162 - 168 2009年4月

記述言語：日本語出版者・発行元：The Crystallographic Society of Japan

The rare-earth iron oxides RFe₂O₄ (R = Y, Ho-Lu) have a rhombohedral crystal structure, consisting of an alternating stacking of triangular lattices of R, Fe and O ions. Recently, we have proposed that this system shows a new mechanism of ferroelectricity ; the ferroelectric state originates from a polar charge-ordered structure of Fe²⁺ and Fe³⁺ on a triangular lattice. In this article, a review is given on the details of this ferroelectricity, which were revealed by measurements of synchrotron X-ray diffraction and dielectric properties of one of the RFe₂O₄ oxides, LuFe₂O₄.

DOI： 10.5940/jcrsj.51.162

その他リンク： https://jlc.jst.go.jp/DN/JALC/00331402115?from=CiNii

Commensurate-incommensurate urate transition of charge density waves in o-TaS3

K. Inagaki, M. Tsubota, K. Ichimura, S. Tanda, K. Yamamoto, N. Hanasaki, Y. Nogami, N. Ikeda, T. Ito, H. Toyokawa

PHYSICA B-CONDENSED MATTER 404 ( 3-4 ) 396 - 398 2009年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We report a synchrotron X-ray study of charge density waves (CDWs) in an o-TaS3 crystal. CDW of o-TaS3 has been known to undergo a commensurate-incommensurate transition at 100 K, below which the wavevector locks in with the pristine lattice. However, the details of the commensurate-incommensurate transition remain open problems, the example being whether the discommensuration exists or not in the neighborhood of the transition. We exploited the beamline BL02B1 of SPring-8. A two-dimensional detector was placed at a distance of 1300mm from the sample, providing an angle resolution of 0.0076 degrees. Temperature dependence of the Bragg peak (0 0 2) and satellite peak (1 - 12) + q was measured from 7 to 180 K. We found that a new phase in the temperature range of 130-50 K, where two independent CDWs coexist. These waves are incommensurate and commensurate CDWs with longitudinal wave vectors q(c) = 0.252c* and 0.250c*, respectively. By lowering the temperature, intensity of the incommensurate CDW was decreased, while that of the commensurate CDW was increased. Below 50K, the incommensurate CDW was completely diminished. Based on the concept of discommensuration, we suggested the dislocation configuration from the intensity of the two CDWs. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2008.11.017

Current-Density Dependence of the Charge-Ordering Gap in the Organic Salt theta-(BEDT-TTF)(2)CsM(SCN)(4) (M = Zn, Co, and Co0.7Zn0.3)

Fumiaki Sawano, Tomohiro Suko, Taichi S. Inada, Shuichi Tasaki, Ichiro Terasaki, Hatsumi Mori, Takehiko Mori, Yoshio Nogami, Naoshi Ikeda, Masashi Watanabe, Yukio Noda

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 ( 2 ) 24714-024714 2009年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We have measured and analyzed the resistivity and voltage-current characteristics of the charge-ordered organic salt theta-(BEDT-TTF)(2)CsM(SCN)(4) (M = Zn, Co, and Co(0.7)Z(0.3)). At 4.3 K, all the samples show giant nonlinear conduction, in which the c-axis resistivity markedly decreases with external current by a factor of 10 against a small electric field of 1 V/cm. The temperature dependence of the resistivity is well described by an activation law, the activation energy of which is evaluated to be 2 meV in the low-current limit, and linearly decreases with external current. The activation energy and x-ray intensity near q(2) = (0, k, 1/2) are found to show the same dependence on current density. This coincidence strongly suggests that the energy gap of the charge order indexed by q(2) is an order parameter of this phenomenon.

DOI： 10.1143/JPSJ.78.024714

Local Structure Analysis of Cubic Perovskite CaCu3Ti4O12

Yasuhiro Yoneda, Kenji Yoshii, Hironori Hayakawa, Naoshi Ikeda

Transactions of the Materials Research Society of Japan 34 ( 1 ) 15 - 15 2009年

記述言語：日本語出版者・発行元：The Materials Research Society of Japan

Recently, there has been considerable interest in the dielectric properties of the cubic perovskite CaCu₃Ti₄O₁₂. The material has shown to have relatively high temperature independent dielectric permittivity over a wide temperature range from 100 K to 600 K. Below ～ 100 K the permittivity drops by almost three orders of magnitude, but is not accompanied by a structural phase transition. We studied CaCu₃Ti₄O₁₂ hoping to find signatures of local structural distortions that may explain the observe anomalies in the dielectric properties. Experiments were carried out using synchrotron radiation at several temperatures between room temperature and 10 K. Reconsideration is necessary for interpreting a huge permittivity by the local disorder model.

DOI： 10.14723/tmrsj.34.15

Nanometer-Sized Domain Structures in LuFeMO4 (M = Cu, Co) Revealed by Energy-Filtered Transmission Electron Microscopy

Y. Matuso, A. Hirata, Y. Horibe, K. Yoshii, N. Ikeda, S. Mori

FERROELECTRICS 380 56 - 62 2009年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

Diluted effect on the charge ordered (CO) structure in dielectric materials LuFeMO4 (M = Cu, Co) were investigated by an energy-filtered transmission electron microscopy (TEM), in combination with a conventional TEM. It is revealed that partial substitution of Cu2+ and Co2+ for Fe2+ in LuFe2O4 destabilized the CO structure. In LuFeCuO4, there exist characteristic zigzag-shaped diffuse streaks and diffuse spots at the h/3-delta h/3-delta 0-type positions (h: integer, delta = 0.06) in reciprocal space, which originate from static cationic ordering of Fe3+ and Cu2+ ions in the triangular lattice. Moreover, real-space images by the energy-filtered TEM revealed that nanometer-sized domain structures with the 5 similar to 10 nm size are formed. In contrast, honeycomb-shaped diffuse streaks were found in LuFeCoO4, in which no domain structures are observed in real-space images.

DOI： 10.1080/00150190902873204

Magnetic and Dielectric Properties of R0.5Ca0.5MnO3 (R = Eu-Lu)

Kenji Yoshii, Yusuke Hiramitsu, Yasuhiro Yoneda, Yuka Okajima, Yasuo Nishihata, Jun'Ichiro Mizuki, Naoshi Ikeda

FERROELECTRICS 379 407 - 414 2009年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

The magnetic and dielectric properties of perovskite manganites R0.5Ca0.5MnO3 (R = Eu-Lu), which show charge ordering of the Mn-3d electrons below room temperature, have been investigated. Their dielectric constants were similar to 1000-10000 at around room temperature. Inflections or peaks of temperature dependences of the dielectric constants were observed at around the charge-ordering temperatures. Analyses of tan delta for R = Eu-Lu and EXAFS spectra for R = Dy suggested that the dielectric properties of the present system are rooted in a special arrangement and transfer of the Mn-3d electrons. The two-peak structure of tan d indicates that dielectric measurement can be used to observe homogeneity or inhomogeneity of sample, as mentioned in our previous paper on the ruthenium perovskite oxides.

DOI： 10.1080/00150190902852208

Stoichiometric Study of the Dielectric and Magnetic Properties in Charge Frustrated System LuFe2O4

Takamasa Michiuchi, Yusuke Yokota, Takuma Komatsu, Hironori Hayakawa, Tomoko Kuroda, Daisuke Maeda, Yoji Matsuo, Shigeo Mori, Kenji Yoshii, Noriaki Hanasaki, Takashi Kambe, Naoshi Ikeda

FERROELECTRICS 378 175 - 180 2009年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

We report dielectric and magnetic properties of a single crystal of LuFe2O4 with different degrees of oxygen deficiency. The oxygen stoichiometry was monitored with the gas mixture ratio of CO2 and CO during the crystal growing process. A sample having high resistivity of about 10 k cm sample was found at room temperature. The relation between the control of the charge frustration and the completeness of the charge ordering is discussed.

DOI： 10.1080/00150190902859187

Synchrotron X-ray study of charge density waves in o-TaS3 査読

Inagaki K, Tsubota M, Ichimura K, Tanda S, Yamamoto K, Hanasaki N, Nogami Y, Ikeda N, Ito T, Toyokawa H

25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 4 150 2009年

RFe2O4の電荷秩序による強誘電性

池田直

日本物理学会誌 64 535 - 539 2009年

Local Structure Modulation in the Electronic Ferroelectric Oxide LuFe2O4

Hironori Hayakawa, Masanori Morimoto, Naoshi Ikeda, Yasuhiro Yoneda, Shinji Kohara, Kenji Yoshii, Yoji Matsuo, Takamasa Michiuchi, Shigeo Mori

Transactions of the Materials Research Society of Japan 34 ( 1 ) 51 - 51 2009年

記述言語：日本語出版者・発行元：The Materials Research Society of Japan

We have investigated the physical properties and local atomic structure of LuFe₂O₄, a material belonging to the multiferroic system RFe₂O₄ (R: rare earths) which shows the new type of ferroelectricity owing to the charge ordering of Fe ions. Magnetic measurements showed the ferromagnetic ordering of Fe spins at ～230 K, as reported previously. From dielectric measurements, the dielectric constant (ε) of ～10000 was obtained at around room temperature. In addition, a peak of ε was observed near the charge-ordering temperature (～330 K). The peak temperature was insensitive to the frequency of AC electric field; this behavior is different from that found in a previous study. The pair-distribution function analysis on a high-energy X-ray diffraction pattern revealed that LuFe₂O₄ has the systematic modulation of the local atomic displacement.

DOI： 10.14723/tmrsj.34.51

Effects of Oxygen Annealing on Dielectric Properties of LuFeCuO4

Yoji Matsuo, Muneyasu Suzuki, Yuji Noguchi, Takeshi Yoshimura, Norifumi Fujimura, Kenji Yoshi, Naoshi Ikeda, Shigeo Mori

JAPANESE JOURNAL OF APPLIED PHYSICS 47 ( 11 ) 8464 - 8467 2008年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：JAPAN SOC APPLIED PHYSICS

We investigated the effect of oxygen annealing on dielectric properties of LuFeCuO4 mainly by dielectric measurements and transmission electron microscopy experiments. It was found that the leakage current density decreases with high-pressure oxygen annealing and the size of nanodomains with orientational polarization increases, which is characterized by the short-range ordering of Fe3+ and Cu2+ ions on a triangular lattice. In addition, the absolute value of relative permittivity epsilon ' decreases with oxygen annealing and epsilon ' exhibits a broad peak in the temperature window between room temperature and 550 K, which is similar to that observed in relaxor ferroelectric materials. The present experimental results suggest that the number of oxygen vacancics has a crucial effect on dielectric properties of LuFeCuO4. [DOI: 10.1143/JJAP.47.8464]

DOI： 10.1143/JJAP.47.8464

Ferroelectric properties of triangular charge-frustrated LuFe(2)O(4)

Naoshi Ikeda

JOURNAL OF PHYSICS-CONDENSED MATTER 20 ( 43 ) 434218 2008年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP PUBLISHING LTD

Magnetic and dielectric correlation in triangular mixed valence iron oxide RFe(2)O(4) is discussed. The frustrated interaction for antiferromagnetic spins as well as charges realizes the auto-organized superlattice cell of iron ions. The characteristic charge and spin superlattice cell drives the magnetoelectric cross-correlation. The charge supercell detected with a resonant x-ray scattering measurement has an electric polarization that forms a class of new ferroelectrics.

DOI： 10.1088/0953-8984/20/43/434218

Temperature and electric-current dependence of charge-ordered domains in θ-(BEDT-TTF)2CsZn(SCN)4

Takayoshi Ito, Masashi Watanabe, Ken-ichiro Yamamoto, Naoshi Ikeda, Yoshio Nogami, Yukio Noda, Hatsumi Mori, Takehiko Mori, Ichiro Terasaki

Europhys. Lett., 84 26002 pp5 (2008) 84 ( 2 ) 26002 2008年10月

Field-induced discommensuration in charge density waves in ο-TaS3

Katsuhiko Inagaki, Masakatsu Tsubota, Kazuki Higashiyama, Koichi Ichimura, Satoshi Tanda, Kenichiro Yamamoto, Noriaki Hanasaki, Naoshi Ikeda, Yoshio Nogami, Takayoshi Ito, Hidenori Toyokawa

J. Phys. Soc. Jpn. 77 093708 pp4 (2008). 77 ( 9 ) 093708 2008年9月

Effect of Oxygen Vacancies on Charge Ordered Structure in YFe2O4-δ

Shigeo Mori, Satoshi Shinohara, Yoji Matsuo, Yoichi Horibe, Kenji Yoshii, Naoshi Ikeda

Jpn. J. Appl. Phys. 47 7595-7598 (2008). 47 ( 9 ) 7595 - 7598 2008年9月

Magnetic and dielectric properties of HoFe2O4 and R1-xRx ' Fe2O4 (R, R ': rare earths)

Kenji Yoshi, Yasuhiro Yoneda, Daisuke Maeda, Yusuke Yokota, Takamasa Michiuchi, Takuma Komatsu, Naoshi Ikeda, Yoji Matsuo, Shigeo Mori

JAPANESE JOURNAL OF APPLIED PHYSICS 47 ( 9 ) 7599 - 7602 2008年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：JAPAN SOC APPLIED PHYSICS

Rare-earth iron oxides of the form RFe2O4 (R = Y, Ho-Lu) show a new mechanism of ferroelectricity owing ot the charge ordering of Fe ions below similar to 330 K. To determine the physical propertie sof the isystem, the magnetic and dielectric properties of HoFe2O4 and R1-xRx'Fe2O4 were investigated (R, R': rare earths). All the materials showed dielectric constants of similar to 100-10000, as reported for some other RFe2O4 oxides. For HoFe2O4, magnetic ordering occurred at a temperature lower than tose of RFe2O4 reported thus for. On the other hand, the dielectric measurements of this material suggested the development of a correlation between polar regions at higher temperatures, which was also observed for the sc-substituted system Lu1-xScxFe2O4. These results encourage detailed investigations of these materials form the viewpoints of both fundamental and applied sciences and suggest the existence of other new properties of RFe2O4.

DOI： 10.1143/JJAP.47.7599

Magnetic and dielectric properties of InFe2O4, InFeCuO4, and InGaCuO4

Kenji Yoshii, Naoshi Ikeda, Yuka Okajima, Yasuhiro Yoneda, Yoji Matsuo, Yoichi Horibe, Shigeo Mori

INORGANIC CHEMISTRY 47 ( 14 ) 6493 - 6501 2008年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

The magnetic and dielectric properties of InFe2O4, InFeCuO4, and InGaCuO4 have been investigated. All these materials are isostructural with RFe2O4 (R = Y, Ho-Lu), which shows ferroelectricity due to iron-valence ordering. InFe2O4 exhibits ferrimagnetic ordering at T-C similar to 242 K and a dielectric constant (epsilon) of similar to 10000 at around room temperature. These properties resemble those of RFe2O4; the origins of the magnetic and dielectric phenomena are likely common in InFe2O4 and RFe2O4. From measurements of the other two materials, we found that both T-C and epsilon are decreased in the order of InFe2O4, InFeCuO4, and InGaCuO4. This result strongly supports the previously reported explanation based on an electron transfer between the Fe-site ions for the corresponding rare-earth systems. Therefore, we propose that the dielectric properties of the oxides isostructural with RFe2O4 are plausibly governed by electron transfer; this situation is different from that of ordinary ferroelectrics and dielectrics, in which the displacement of cations and anions is important. In addition, InFeCuO4 and InGaCuO4 exhibit large epsilon values (epsilon > similar to 1500). In consideration of this property, we discuss the possible applications of these oxides.

DOI： 10.1021/ic702365k

Non-thermal evidence for current-induced melting of charge order in theta-(BEDT-TTF)(2)CsZn(SCN)(4)

Masashi Watanabe, Kenichiro Yamamoto, Takayoshi Ito, Yusaku Nakashima, Makoto Tanabe, Noriaki Hanasaki, Naoshi Ikeda, Yoshio Nogami, Hiroyuki Ohsumi, Hidenori Toyokawa, Yukio Noda, Ichiro Terasaki, Fumiaki Sawano, Tomohiro Suko, Hatsumi Mori, Takehiko Mori

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 ( 6 ) 65004 2008年6月

Electronic ferroelectricity from charge ordering in RFe2O4

Naoshi Ikeda, Yoji Matsuo, Shigeo Mori, Kenji Yoshi

IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL 55 ( 5 ) 1043 - 1045 2008年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

We report our recent discovery of novel ferroelectricity arising from the polar ordering of Fe3+ and Fe2+ in a mixed valence triangular lattice oxide LuFe2O4, where the electric polarization is not a result of ionic displacement. The polar ordering of Fe3+ and Fe2+ was confirmed with a resonant x-ray scattering study in SPring-8. The origin of such ordering is the competitive interaction between Fe3+ and Fe2+ in the triangular lattice, i.e., the charge frustration. The polar superlattice of Fe3+ and Fe2+ develops below 350 K, where the electric polarization appears. The ferro electricity arising from the polar charge ordering or the polar electron distribution may have great potential for the future application of ferroelectrics.

DOI： 10.1109/TUFFC.2008.753

三角格子系鉄複合酸化物LuFe_2O_4における電荷秩序構造と誘電特性

松尾祥史, 吉井賢資, 池田直, 森茂生

日本結晶学会誌 50 ( 2 ) 150 - 154 2008年4月

記述言語：日本語出版者・発行元：The Crystallographic Society of Japan

Recent works revealed that a ferroelectric polarization in the charge-frustrated system LuFe₂O₄ originates from an emergence of the charge ordering, which is characterized by a regular arrangement of Fe²⁺ and Fe³⁺ ions on the frustrated triangular lattice. In this work, we have investi-gated both the charge ordered (CO) structure and charge ordering processes mainly by means of the transmission electron microscopy (TEM) . Both the CO structure and charge ordering processes depend strongly on the amount of the oxygen deficiency (δ) involved in LuFe₂O_4-δ. In the case of δ-0, the three-dimensional CO structure with the modulation vector of q= [1/3 1/3 1/2] was formed at room temperature. On the other hand, as δ was increased, the three-dimensional CO structure changed into the two-dimensional CO one and the coherent length becomes shorter along the [001] direction. For proper understanding of the dielectric and magnetic properties in LuFe₂O₄ and related materials, it should be essential to prepare LuFe₂O_4-δ samples with properly controlled oxygen-concentration and elucidate the physical properties in LuFe₂O_4-δ with δ-0.

DOI： 10.5940/jcrsj.50.150

その他リンク： https://jlc.jst.go.jp/DN/JALC/00313809260?from=CiNii

NaV_2O_5の逐次電荷不均化による悪魔の花 : 悪魔の花を咲かせる Ising スピンの詳細と競合する相互作用の理解

大和田謙二, 藤井保彦, 村岡次郎, 中尾裕則, 村上洋一, 野田幸男, 大隅寛幸, 池田直, 菖蒲敬久, 礒部正彦, 上田寛

放射光 21 ( 2 ) 87 - 96 2008年3月

Relaxation of geometrical frustration in NbSe3 topological crystals

Taku Tsuneta, Yoshio Nogami, Kenichirou Yamamoto, Naoshi Ikeda, Satoshi Tanda

ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES 64 C509 - C509 2008年

Dilution effect on microstructures with respect to magnetic and dielectric properties in charge-ordered ferroelectric LuFe(2)O(4)

Y. Matsuo, Y. Horibe, K. Yoshii, N. Ikeda, S. Mori

TRANSACTIONS OF THE MATERIALS RESEARCH SOCIETY OF JAPAN, VOL 33, NO 1 33 ( 1 ) 31 - 34 2008年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：MATERIALS RESEARCH SOCIETY JAPAN-MRS-J

We investigated magnetic/dielectric properties and related microstructures in LuFeCuO(4), which was obtained by substituting Cu(2+) for Fe(2+) in LuFe(2)O(4). It was found that LuFeCuO(4) shows a characteristic low-frequency dielectric dispersion around 300K. We analyzed it using the Debye model and found that LuFeCuO(4) is a dielectric compound with an orientational polarization. Electron diffraction experiments revealed that there exists characteristic zigzag-shaped diffuse scattering in LuFeCuO(4). In addition, we found the presence of nano-sized domains, which consist of a short-range ordering of Fe(3+) and Cu(2+) on the triangular lattice. The present results suggest that the short-range ordering gives rise to some anomalous dielectric properties in LuFeCuO(4).

Magnetic and dielectric properties of Tb0.5Ca0.5MnO3

Yusuke Hiramitsu, Kenji Yoshii, Yasuhiro Yoneda, Jun'ichiro Mizuki, Akio Nakamura, Yutaka Shimojo, Yoshinobu Ishii, Yukio Morii, Naoshi Ikeda

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 46 ( 10B ) 7171 - 7174 2007年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：INST PURE APPLIED PHYSICS

The magnetic and dielectric properties of a perovskite manganite Tb0.5Ca0.5MnO3 were investigated. Magnetic measurements showed three characteristic temperatures, originating from charge, ordering (similar to 360K), antiferromagnetic ordering (similar to 120K), and a transition to a glassy state (similar to 50 K). The coexistence of the charge and antiferromagnetic orderings was confirmed by powder neutron diffraction. AC dielectric measurements showed large dielectric constants larger than similar to 1000 at approximately room temperature. The temperature dependence of the dielectric constant changed just below the charge-ordering temperature. From the analysis of tan delta, the activation energy for switching the directions of polar regions was calculated to be similar to 0.09 eV, which is close to the activation energy of the Mn 3d electron transfer. These results strongly suggest that the dielectric properties of this material are governed by the ordering and transfer of the Mn 3d charges.

DOI： 10.1143/JJAP.46.7171

Lattice modulation in YMn2O5 and TbMn2O5 studied by using synchrotron radiation X-rays

Y. Noda, H. Kimura, Y. Kamada, Y. Ishikawa, S. Kobayashi, Y. Wakabayashi, H. Sawa, N. Ikeda, K. Kohn

JOURNAL OF THE KOREAN PHYSICAL SOCIETY 51 ( 2 ) 828 - 831 2007年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：KOREAN PHYSICAL SOC

RMn2O5 (R = Y and rare earth) shows successive magnetic and ferroelectric phase transitions at about 45 K, 40 K, 39 K, 20 K and 10 K and is called a multiferroic compound. We have investigated the lattice modulation vectors (qL) of YMn2O5 and TbMn2O5 by using single crystal Synchrotron Radiation X-ray diffraction and compared them with the magnetic propagation vectors (qM) studied by neutron diffraction. The relation of the propagation vectors between magnetic materials and dielectrics is found to be qL = 2qM. A preliminary structure analysis of the atomic displacement pattern in the commensurate ferroelectric phase of TbMn2O5 is discussed.

Magnetic and dielectric properties of RFe2O4, RFeMO4, and RGaCuO4 (R=Yb and Lu, M=Co and Cu)

Kenji Yoshii, Naoshi Ikeda, Yoji Matsuo, Yoichi Horibe, Shigeo Mori

PHYSICAL REVIEW B 76 ( 2 ) 1 - 12 2007年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The magnetic and dielectric properties have been investigated for the isostructural oxides of RFe2O4, RFeMO4, and RGaCuO4 (R=Yb and Lu, M=Co and Cu). The magnetization measurements for RFe2O4 showed ferrimagnetic ordering at similar to 250 K. This system also exhibited large dielectric constants of similar to 10 000-30 000 at around room temperature, which is attributable to the charge-ordering-induced ferroelectricity, as was proposed in our recent paper. The magnetic transition temperatures are lowered to similar to 45-90 K for RFeMO4. Magnetic ordering is not found for RGaCuO4. ac magnetic susceptibility measurements indicate that magnetic ordering becomes short-ranged by the substitution at the Fe site. The overall characteristic behavior of the magnetic properties is explained in terms of the change of a spin value as well as the dilution of magnetic interactions. Although the ac dielectric measurements show the existence of polar regions in each material, the dielectric constants below 300 K become smaller in the order of RFe2O4, RFeCoO4, RFeCuO4, and RGaCuO4. From the analysis of the dielectric dispersion, the distribution of the fluctuation time of polar regions is wider in RFeCoO4, RFeCuO4, and RGaCuO4 than in RFe2O4; a coherent motion of polar regions is suppressed in the substituted systems. By comparison to the results from the magnetic measurements, the dielectric properties are discussed in connection with a charge transfer between the transition-metal 3d orbitals, consistently with the proposed mechanism of the ferroelectricity in RFe2O4.

DOI： 10.1103/PhysRevB.76.024423

Magnetic and dielectric behavior of TmFe2O4 and TmFeCuO4

Kenji Yoshii, Naoshi Ikeda, Shigeo Mori

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 ( 2 ) 1154 - 1156 2007年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The magnetic and dielectric properties are investigated for TmFe2O4 and TmFe2CuO4. The properties of TmFe,04, which shows the ferroelectricity from iron-valence ordering, are essentially the same as those of the other RFe2O4 oxides, i.e., ferrimagnetic ordering at around 250 K and dielectric constants larger than 3000 at around room temperature. On the other hand, the Cu-substituted oxide TmFeCuO4 shows no magnetic transition and considerably smaller dielectric constants. The change of the properties is likely attributable to a reduction of a charge transfer between the transition-metal ions. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.327

Structural properties of a mixed valence compound Fe2BO4

S. Shimomura, S. Nakamura, N. Ikeda, E. Kaneko, K. Kato, K. Kohn

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 ( 2 ) 793 - 795 2007年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We have performed X-ray powder diffraction measurements in a mixed valence compound of Fe2BO4 using synchrotron radiation. The diffraction patterns obtained at several temperatures between 85 and 386K were analyzed by the Rietveld method. The monoclinic-orthorhombic transition, ascribed to charge-ordering of Fe2+ and Fe3+ ions, was confirmed by the temperature dependence of the monoclinic angle beta. No superlattice reflection due to the charge-ordering was detected. The temperature dependences of the lattice parameters show anomalies around 270K as well as the monoclinic-orthorhombic transition temperature of 327-347K. The structural change around 270K is attributable to the onset of the partial charge-delocalization. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.184

Structural relations between two ground states of NaV₂O₅ under high pressure: A synchrotron x-ray diffraction study

K. Ohwada, Y. Fujii, J. Muraoka, H. Nakao, Y. Murakami, Y. Noda, H. Ohsumi, N. Ikeda, T. Shobu, M. Isobe, Y. Ueda

Physical Review B 76 ( 9 ) 094113 2007年

<bold>Electronic Ferroelectricity from Charge Ordering in RFe2O4</bold> 査読

N. Ikeda, S. Mori, K. Yoshii, Y. Matsuo

2007 SIXTEENTH IEEE INTERNATIONAL SYMPOSIUM ON THE APPLICATIONS OF FERROELECTRICS, VOLS 1 AND 2 253 - + 2007年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IEEE

We report a novel ferroelectricity arise from the polar ordering of Fe3+ and Fe2+ in a mixed valence triangular lattice oxide LuFe2O4, where the electric polarization do not arise from the ionic displacement. The polar ordering of Fe3+ and Fe2+ was confirmed with a resonant X-ray scattering study in SPring-8. The origin of such ordering is the competitive C, interaction between Fe3+ and Fe2+ in the triangular lattice, i.e. the charge frustration. The polar superlattice of Fe3+ and Fe2+ develops below 350K where the electric polarization appears. The ferroelectricity arising from the polar charge ordering or the polar electron distribution may have a great potential for the future application of ferroelectrics.

Magnetic and Dielectric Properties of Rare-Earth Iron and Manganese Oxide Systems

K. Yoshii, N. Ikeda

Focus on Solid State Chemistry (Ed. by Arte M. Newman) 63 - 75 2007年

Ferroelectricity from electron ordering

N. Ikeda, S. Mori, K. Yoshii, Y. Matsuo

Mater. Res. Symp. Proc 966 ( 0966-T01-03 ) 1 - 9 2007年

Ferroelectricity from valence ordering in RFe2O4

Naoshi Ikeda, Shigeo Mori, Kenji Yoshii

FERROELECTRICS 348 440 - + 2007年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

We report a polar ordering of electrons in RFe2O4, which consistently explains the ferroelectric property of this material. Pyroelectric current measurement, low frequency AC dielectric constants, resonant X-ray scattering diffraction experiment and the consideration for the charge frustration, consistently lead the presence of ferroelectricity originated from the ordering of Fe3+ and Fe2+. The ferroelectric material originated from the polar electron distribution and free from the ionic displacement may potentially have great possibilities in future applications and fundamental researches.

DOI： 10.1080/00150190701196112

Structural phase transition in two-dimensional crystallites of organic dye molecules formed on aqueous subphases

Noritaka Kato, Ichiro Hirosawa, Masugu Sato, Naoshi Ikeda, Ken-Ichi Iimura, Yoshiaki Uesu

Ferroelectrics 346 162 - 167 2007年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

The 2D crystallites of polar organic dye molecules on an aqueous subphase exhibit a thermochromic phase transition. The visible absorption band of the crystallites depends on the temperature and the composition of the subphase. In-situ observations of the phase transition were carried out by a grazing incidence X-ray diffraction method. A shift and a split of the diffraction peaks were observed between the different phases, indicating a change in the molecular arrangement of the crystallites in their chromic transition.

DOI： 10.1080/00150190601182477

Magnetic and dielectric behavior of Magnetic and Dielectric Behavior of the Ruthenium Double Perovskite Oxides R2MRuO6 (R=La, Pr and Nd, M=Mg, Co, Ni and Zn)

K. Yoshii, N. Ikeda, S. Mori, Y. Yoneda, M. Mizumaki, H. Tanida, Naomi Kawamura

Trans. Mater. Res. Soc. Jpn. 32 ( 1 ) 51 - 54 2007年

Lattice modulation induced by antiferromagnetic orderings in multiferroic RMn₂O₅

Hiroyuki KIMURA, Satoru KOBAYASHI, Youichi KAMADA, Yoshihisa ISHIKAWA, Kohei KADOSHITA, Yukio NODA, Naoshi IKEDA, Yusuke WAKABAYASHI, Kay KOHN

Photon Factory Activity Report 24 ( B ) 176 2007年

Doping effect on the charge ordering in LuFe2O4

Yoji Matsuo, Satoshi Shinohara, Shigeo Mori, Yoichi Horibe, Kenji Yoshii, Naoshi Ikeda

Materials Research Society Symposium Proceedings 966 22 - 27 2006年12月

Change of the charge ordered (CO) structure by substituting Cu2+ for Fe2+ in LuFe2O4 was investigated by means of the transmission electron microscopy. The CO structure in LuFe 2O4 is characterized by the modulated structure with the wave vector of q=1/3[1-13/2] and the average size of the CO domains can be estimated to be about 10-20nm. On the contrary, the Cu substitution in LuFe 2O4 destroyed the CO structure drastically and induced characteristic local lattice distortion, which gives rise to characteristic diffuse scattering in the reciprocal space. High-resolution lattice images revealed that there exist nano-scale clusters, which are characterized as the short-range ordering of the Fe3+ and Cu2+ ions on the triangular lattice. In addition, the magnetic measurement revealed that LuFeCuO4 exhibits an antiferromagnetic transition around 50K, which is lower than the Neel temperature of 250K in LuFe2O4. © 2007 Materials Research Society.

Relation between ferroelectric and antiferromagnetic order in RMn2O5

Yukio Noda, Hiroyuki Kimura, Youichi Kamada, Toshihiro Osawa, Yosikazu Fukuda, Yoshihisa Ishikawa, Satoru Kobayashi, Yusuke Wakabayashi, Hiroshi Sawa, Naoshi Ikeda, Kay Kohn

PHYSICA B-CONDENSED MATTER 385 119 - 122 2006年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

RMn2O5 (R = Y and rare earth) shows successive magnetic and ferroelectric phase transitions at about 45, 40, 39, 20 and 10 K. We have reinvestigated the magnetic structure of YMn2O5 at the commensurate phase (T = 25 K) using a single crystal four-circle diffractometer in order to discuss the mechanism of magnetoelectric interaction and the origin of ferroelectricity. We also observed the lattice modulation vectors (q(L)) to compare the magnetic propagation vectors (q(M)) by synchrotron X-ray diffraction. Improved magnetic structure data are compared with the theory recently proposed. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.05.179

Magnetic and dielectric properties of the ruthenium double perovskites La2MRuO6 (M = Mg, Co, Ni, and Zn)

Kenji Yoshii, Naoshi Ikeda, Masaichiro Mizumaki

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 203 ( 11 ) 2812 - 2817 2006年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-V C H VERLAG GMBH

Magnetic and dielectric properties of the ruthenium double perovskites La2MRuO6 (M = Mg, Co, Ni, and Zn) were investigated. The magnetization measurements for M = Co and Ni showed the existence of magnetic order at 20-30 K. Though the oxides with M = Zn and Mg exhibit a deviation from the Curie-Weiss law, magnetic order was not clearly observed. The result of La2ZnRuO6 was different from that previously reported, in which a ferromagnetic transition was found at around 165 K. The AC dielectric measurements for M = Co and Ni showed large dielectric constants (typically larger than 1000) at around room temperature, suggesting both the formation of short-ranged polar regions and the magnetic origin of large dielectric constant. In addition, two peaks were found for the temperature dependence of the tan delta component for La2NiRO6. The behavior suggests the existence of two different polar regions. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.200669549

Resonant X-ray scattering study at YK-edge in Y1-xCaxTiO3

Hironori Nakao, Soukichi Kodama, Kouhei Kiyoto, Youichi Murakami, Masami Tsubota, Fumitoshi Iga, Kazuyuki Uchihira, Toshiro Takabatake, Hiroyuki Ohsumi, Masaichiro Mizumaki, Naoshi Ikeda

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 ( 9 ) 2006年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Resonant X-ray scattering (RXS) in Y1-xCaTiO3 has been investigated near the Y K-edge. The resonant signal has been clearly found at a forbidden reflection, (500), and the intensity shows an azimuthal angle dependence with a twofold symmetry. The RXS intensities have almost no Ca concentration dependence, although the RXS intensities at the Ti K-edge markedly decrease with increasing Ca concentration. The origin of the RXS at the Y K-edge is clarified to be the deviation from 180 degrees of the Ti-O-Ti bond angle, namely, the tilts of the octahedra around the Y ion. We also discuss the RXS mechanism at the main edge of the Ti K-edge.

DOI： 10.1143/JPSJ.75.094706

Erratum: Spontaneous formation of vanadium "molecules" in a geometrically frustrated crystal: AlV2O4 ( Physical Review Letters (2006) 96 (086406))

Y. Horibe, M. Shingu, K. Kurushima, H. Ishibashi, N. Ikeda, K. Kato, Y. Motome, N. Furukawa, S. Mori, T. Katsufuji

Physical Review Letters 96 2006年5月

Direct determination of low-dimensional structures: Synchrotron X-ray scattering on one-dimensional charge-ordered MMX-chain complexes

Yusuke Wakabayashi, Atsushi Kobayashi, Hiroshi Sawa, Hiroyuki Ohsumi, Naoshi Ikeda, Hiroshi Kitagawa

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 ( 20 ) 6676 - 6682 2006年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

A powerful method to determine the hidden structural parameters in functional molecules has been developed. Local valence arrangements that dominate the material properties are sometimes not three-dimensionally ordered. This method that comprises diffuse X-ray scattering and resonant X-ray scattering is suitable in such cases. Using this method, we present clear evidence of the low-dimensional valence arrangement in two halogen-bridged one-dimensional metal complexes, so- called MMX chains. This family allows us to control many physical and structural parameters by chemical substitution of bridging halogen, counterions, or metal ions, and one of our samples carries an unusual metallic phase. It is demonstrated with this complex that the present method makes it possible to have microscopic insight to low-dimensionally ordered systems.

DOI： 10.1021/ja060111j

Magnetic and dielectric properties of frustrated ferrimagnet TmFe2O4

K Yoshii, N Ikeda, A Nakamura

PHYSICA B-CONDENSED MATTER 378-80 585 - 586 2006年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The magnetic and dielectric properties of TmFe2O4 were investigated. Magnetization measurements showed a ferrimagnetic transition around 240 K. A modulation of this ordering with a slow spin relaxation was found below similar to 70-100 K. A characteristic low-frequency dielectric dispersion was also obtained, which is analogous behavior to that for a few other RFe2O4 oxides reported previously. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.155

Structure and random anisotropy in single-phase Ni nanocrystals

E Kita, N Tsukuhara, H Sato, K Ota, H Yangaihara, H Tanimoto, N Ikeda

APPLIED PHYSICS LETTERS 88 ( 15 ) 2006年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

We prepared high-purity oxygen-free and single-phase Ni nanocrystals using the gas condensation and deposition method in order to examine the random anisotropy model (RAM). The grain size of an as-prepared sample was estimated to be 8-10 nm. Thermal annealing increased grain sizes (D) up to 22 nm. Clear D-6 dependence of the coercive force on a grain size smaller than 13 nm was obtained for samples prepared on both plastic and KBr single-crystal substrates. For larger grain sizes, H-c decreased with D-1 and these results clearly conform to the RAM in single-element nanocrystal systems. A local anisotropy constant was estimated from the slope of the D-6 relation and the peak of H-c at D=13 nm. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2188597

Spontaneous formation of vanadium “molecules” in a geometrically frustrated compound: AlV2O4

Y. Horibe, M. Shingu, K. Kurushima, H. Ishibashi, N. Ikeda, K. Kato, Y. Motome, N. Furukawa, S. Mori, T. Katsufuji

Phys. Rev. Lett 96 ( 8 ) 2006年3月

X-ray Diffuse Scattering Study of Modulated Structure in θ-(BEDT-TTF)₂CsM'(SCN)₄ Under Electric Field

Y. Nogami, Masashi Watanabe, Naoshi Ikeda, T. Ito, K. Yamamoto, Yukio Noda, I. Terasaki, H. Mori, T. Mori

SPring-8 User Experiment Reports 2005A 2006年

X-ray and neutron transparent pulse magnets

E. Ohmichi, N. Ikeda, Y. Nogami, T. Osada

YAMADA CONFERENCE LX ON RESEARCH IN HIGH MAGNETIC FIELDS 51 498 - + 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

A new type of pulse magnet, x-ray and neutron transparent pulse magnet, is suggested for use in high-field diffraction experiments. The magnet is made of aluminum-based material, so we expect that the scattered beam penetrates the magnet body and hence the total number of reflection points available substantially increases. This feature possibly allows full determination of the lattice and magnetic structure in strong magnetic fields. To realize this idea, we constructed a prototype transparent magnet consisting of aluminum wire and duralumin reinforcement. With a portable capacitor bank, the maximum field of 25 T was successfully generated in a 1.6 mm bore, even though the aluminum wire is less strong and less conducting than copper wire. Since the total energy is small (E-bank similar to 100 J), high repetition rate, which is necessary for sufficient signal-to-noise ratio, is realized. Technical details, coil performance, and future prospects will be described.

DOI： 10.1088/174-6596/51/1/113

Conduction characteristics of charge ordering type ferroelectrics,YFe2O

K. Imamura, Y. Horibe, T. Yoshimura, N. Fujimura, S. Mori, N. Ikeda

Materials Research Society Symposium Proceedings 966 210 - 216 2006年

Development of X-ray Analysis Method for Topological Crystals

K. Yamamoto, T. Ito, N. Ikeda, S. Horita, N. Irie, Y, Nogami T. Tsuneta, S. Tanda

Topology in Ordered Phase (World Scientific) 86-94 2006年

Structure Analysis of Topological Crystal using Synchrotron Radiation

Y. Nogami, T. Tsuneta, K. Yamamoto, N. Ikeda, T. Ito, N. Irie, S. Tanda

Topology in Ordered Phase (World Scientific) 52-57 2006年

X-ray structural study of charge and anion orderings of TMTTF salts

Y Nogami, T Ito, K Yamamoto, N Irie, S Horita, T Kambe, N Nagao, K Oshima, N Ikeda, T Nakamura

JOURNAL DE PHYSIQUE IV 131 39 - 42 2005年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：EDP SCIENCES S A

High resolution X-ray structure analyses and electronic structure calculation revealed the condition for the charge ordering(CO) observed in the (TMTTF)(2)X (Fabre) salts. The phase diagram of the electronic states including 2k(F) and 4k(F) CO has been proposed associated with magnitudes Of Molecular dimerization and tetramerization.

DOI： 10.1051/jp4:2005131008

Structure, magnetism and transport of the perovskite manganites Ln(0.5)Ca(0.5)MnO(3) (Ln = Ho, Er, Tm, Yb and Lu)

K Yoshii, H Abe, N Ikeda

JOURNAL OF SOLID STATE CHEMISTRY 178 ( 12 ) 3615 - 3623 2005年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE

It was found that the manganese perovskite oxides Ln(0.5)Ca(0.5)MnO(3) (Ln = Ho, Er, Tm, Yb and Lu) have an orthorhombic structure (space group Pnma). The Mn-O-Mn angles were calculated to be similar to 148-150 degrees, revealing an existence of a large crystallographic distortion in these oxides. Electrical resistivity measurements indicated both an insulating nature and a small magnetoresistance effect, both of which are owing to narrow bandwidths of the Mn-3d electrons arising from the crystallographic distortion. DC magnetization measurements showed the three characteristic temperatures, which could be assigned to charge-order, antiferromagnetism or Mn moments, and possible glassy states. All of these temperatures were decreased for the heavier Ln ions, which is explained in connection with both a difference of ionic radii of Ln(3+) and Ca2+, and a lowering of electron transfer. The charge-ordering transition was not clearly observed only for Lu0.5Ca0.5MnO3 containing the smallest lanthanide ion, plausibly due to a large randomness of magnetic interactions arising from the ionic radii difference of Lu3+ and Ca2+. In addition, preliminary measurements of AC dielectric response suggested that these manganites belong to a so-called multiferroic system. (C) 2005 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jssc.2005.08.033

Nano-sized domains related to dielectric anomaly in YFe2O4-δ

Y. Horibe, K. Kishimoto, S. Mori, N. Ikeda

J. Electron Microsc. 54 I87 - I90 2005年9月

Ferro-type orbital state in the mott transition system Ca2-xSrxRuO4 studied by the resonant X-ray scattering interference technique

M Kubota, Y Murakami, M Mizumaki, H Ohsumi, N Ikeda, S Nakatsuji, H Fukazawa, Y Maeno

PHYSICAL REVIEW LETTERS 95 ( 2 ) 2005年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

We have succeeded in detecting ferro-type orbital states in Ca2-xSrxRuO4, which is the first outcome in a 4d Mott transition system by the resonant x-ray scattering interference technique. For x=0 (Mott insulator), the resonant signal for d(xy) orbital ordering is observed even at room temperature, in which the Jahn-Teller distortion is negligible. The signal disappears near the metal-insulator transition. On the other hand, in a metallic phase for x=0.5, orbital polarization with d(yz/zx) character dominates. With lowering temperature, the magnitude of the resonant signal slightly decreases owing to the additional influence of the gamma band with d(xy) character.

DOI： 10.1103/PhysRevLett.95.026401

Structural properties and phase transition of hole-orbital-ordered (C2H5NH3)(2)CuCl4 studied by resonant and non-resonant x-ray scatterings under high pressure

K Ohwada, K Ishii, T Inami, Y Murakami, T Shobu, H Ohsumi, N Ikeda, Y Ohishi

PHYSICAL REVIEW B 72 ( 1 ) 2005年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The effects of hydrostatic pressure on a structure and the corresponding resonant x-ray scattering (RXS) spectrum have been investigated for the hole-orbital-ordered compound (C2H5NH3)(2)CuCl4. We have found a structural phase transition at P-c similar to 4 GPa, as suggested by the Raman scattering measurement, by observing a peak splitting resulting from an orthorhombic-to-monoclinic symmetry breaking. The reduction of the Jahn-Teller distortion (JTD) toward P-c is also ascertained by structural analyses. The gradual change in the color of the crystal is also observed in connection with the structural change near P-c. The red-colored transparency of the crystal indicates that the system is still insulative above P-c. The observed RXS and fluorescence spectrum at ambient pressure were precisely analyzed. We experimentally confirmed that the RXS intensity comes from the polarization of the density of states of p(x) and p(y) symmetries, which is mainly dominated not by the on-site 3d-4p Coulomb interaction but by the JTD of the CuCl6 octahedron. charged Cl ions neighboring the Cu site. It is also expected that the RXS intensity is proportional to JTD; however, our RXS study under a high pressure shows no striking change as JTD is suppressed by the application of pressure. On the other hand, the RXS intensity becomes zero above P-c. The results indicate that the local environment of the Cu2+ ion markedly changes. Two possible structures of EA(2)CuCl(4) above P-c are proposed.

DOI： 10.1103/PhysRevB.72.014123

Determination of a merocyanine J-aggregate structure and the significant contribution of the electric dipole interaction to the exciton band wavelength

N Kato, K Yuasa, T Araki, Hirosawa, I, M Sato, N Ikeda, K Iimura, Y Uesu

PHYSICAL REVIEW LETTERS 94 ( 13 ) 2005年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The molecular alignment of a merocyanine (MC) J-aggregate monolayer at the air-water interface was determined by a grazing incidence x-ray diffraction method. The obtained molecular arrangement apparently shows that the conventional formula, which accounts only for the transition dipole interaction, is not sufficient to figure out the exciton band wavelength, suggesting the importance of the electric dipole (ED) interaction. We derived a simple formula for the ED interaction energy under an extended dipole approximation and clarified the ED contribution in the MC J aggregate.

DOI： 10.1103/PhysRevLett.94.136404

Structural phase transitions and dielectric anomaly in YFe2O4-delta

Y Horibe, K Kishimoto, S Mori, N Ikeda

JOURNAL OF THE KOREAN PHYSICAL SOCIETY 46 ( 1 ) 192 - 194 2005年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：KOREAN PHYSICAL SOC

We examined structural changes related to charge ordering (CO) in the temperature window between 100 K and room temperature (BT) in YFe2O4-delta by transmission electron microscopy. Characteristic diffuse scattering elongated along the [001] direction through the (1/3 1/3 0)-type reciprocal positions was found at RT, which is related to the microdomains due to the CO with a size of 10 - 20 run. In addition, it was also found that the superlattice structures characterized by the (1/3 - eta1/3 + eta0)-type modulation vector, which should be due to the vacancy ordering, coexist with the microdomains due to the CO. On the other hand, in stoichimetric YFe2O4, We found temperature variations of the superlattice structures on warming from 100 K, which should be strongly related to the dielectric anomalies in YFe2O4.

Grazing incidence X-ray diffraction of merocyanine J-aggregate monolayers at the air-water interface

N. Kato, K. Yuasa, T. Araki, Y. Uesu, I. Hirosawa, M. Sato, N. Ikeda, K. Iimura

Trans. Mat. Res. Soc. Jpn. 2005年

Charge ordering and dielectric dispersion in mixed valence oxides RFe2O4

N Ikeda, S Mori, K Kohn

FERROELECTRICS 314 41 - 56 2005年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

In a series of oxides RFe2O4 (R = rare earth between Dy and Lu, or Y), equal numbers of Fe2+ and Fe3+ are located on a layer composed of two triangular nets stacked together. These oxides have several phase transitions where the arrangement of Fe2+ and Fe3+ ions transforms from one type to another. Unique dielectric properties of these oxides have been explained in connection with the charge ordering.
Recent developments on the structure of the ordered phases are reviewed with comments on their correlation with the observed dielectric dispersion.

DOI： 10.1080/00150190590926085

Structural phase transition of J-aggregate crystallites on the binary counter-ion subphase

N Kato, T Araki, Y Uesu, M Sato, Hirosawa, I, N Ikeda, K Iimurac

FERROELECTRICS 314 135 - 141 2005年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

The recently found chromic phase transition of merocyanine J-aggregates monolayer on the aqueous subphase containing Cd2+ and Mg2+ was investigated by the grazing incidence X-ray diffraction method. The evidence of the structural difference between the phases of J-band at 620 nm and 590 nm was obtained by the investigations on the monolayers prepared at the different molar ratios of Cd2+ and Mg2+. The change in a Bragg's peak was observed at the ratio of the ions, where the J-band wavelength also exhibited the discrete shift. The relationship between the obtained results and the phase diagram determined by the shift of the J-band wavelength was also discussed from the viewpoint of the formation mechanism of J-aggregate crystallites.

DOI： 10.1080/00150190590926319

Diffuse Scattering in θ-(BEDT-TTF)₂CsZn(SCN)₄ under Electric Field at Low temperature

N. Ikeda, M. Watanabe, T. Ito, Y. Nogami, S. Komiyama, Y. Noda, I. Terasaki, H. Mori, T. Mori

SPring-8 User Experiment Report 14 301 - 301 2005年

Decrease in X-ray diffuse scattering intensity reflecting two-fold structural modulation in θ-(BEDT-TTF)₂CsZn(SCN)₄ under Electric Field

Y. Nogami, M. Watanabe, N. Ikeda, T. Ito, K. Yamamoto, Y. Noda, I. Terasaki, H. Mori, T. Mori

SPring-8 User Experiment Report 15 18 - 18 2005年

Spin-Peierls Transition in Halogen-Bridged Mixed-Valence MMX Chain Compounds

Koshiro Toriumi, Minoru Mitsumi, Yuji Yoshida, Akihisa Kohyama, Naoshi Ikeda, Nobuhiro Yasuda, Yoshiki Ozawa

ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES 61 C327 - C327 2005年

Structural properties and phase transition of hole-orbital-ordered (C2H5NH3)2CuCl4 studied by resonant and non-resonant x-ray scatterings under high pressure 査読

Kenji Ohwada, Kenji Ishii, Toshiya Inami, Youichi Murakami, Takahisa Shobu, Hiroyuki Ohsumi, Naoshi Ikeda, Yasuo Ohishi

Physical Review B - Condensed Matter and Materials Physics 72 ( 1 ) 2005年

記述言語：英語掲載種別：研究論文（学術雑誌）

The effects of hydrostatic pressure on a structure and the corresponding resonant x-ray scattering (RXS) spectrum have been investigated for the hole-orbital-ordered compound (C2H5NH3)2CuCl4. We have found a structural phase transition at Pc∼4GPa, as suggested by the Raman scattering measurement, by observing a peak splitting resulting from an orthorhombic-to-monoclinic symmetry breaking. The reduction of the Jahn-Teller distortion (JTD) toward Pc is also ascertained by structural analyses. The gradual change in the color of the crystal is also observed in connection with the structural change near Pc. The red-colored transparency of the crystal indicates that the system is still insulative above Pc. The observed RXS and fluorescence spectrum at ambient pressure were precisely analyzed. We experimentally confirmed that the RXS intensity comes from the polarization of the density of states of px and py symmetries, which is mainly dominated not by the on-site 3d-4p Coulomb interaction but by the JTD of the CuCl6 octahedron. charged Cl ions neighboring the Cu site. It is also expected that the RXS intensity is proportional to JTD
however, our RXS study under a high pressure shows no striking change as JTD is suppressed by the application of pressure. On the other hand, the RXS intensity becomes zero above Pc. The results indicate that the local environment of the Cu2+ ion markedly changes. Two possible structures of EA2CuCl4 above Pc are proposed. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevB.72.014123

Dielectric anomaly and structural phase transitions in YFe 2O4-δ

Y. Horibe, K. Kishimoto, S. Mori, N. Ikeda

Integrated Ferroelectrics 67 151 - 157 2004年12月

We examined structural changes related to the charge ordering (CO) in the temperature window between 100K and room temperature (RT) in YFe2O4-δby transmission electron microscopy. Characteristic diffuse scattering elongated along the [001] direction through the (1/3 1/3 0)-type reciprocal positions was found at RT, which is related to nano-sized domains due to the CO. In addition, we found the presence of the superlattice structures characterized by the (1/4 1/4 0)-type modulation vector at 150K and by the (0 1/2 0)-type modulation vector at 200 K. The changes in the superlattice structures as a function of the temperature should be strongly related to the dielectric anomalies in YFe2O4-δ.

DOI： 10.1080/10584580490898876

Structural change on the magnetic field-induced insulator-to-metal transition in distorted perovskite Eu<inf>0.6</inf>Sr<inf>0.4</inf>MnO <inf>3</inf>

Shin Nakamura, Shin Nakamura, Susumu Shimomura, Naoshi Ikeda, Shigeki Nimori, Takao Takeuchi, Kikuo Itoh

Journal of the Physical Society of Japan 73 ( 11 ) 3059 - 3063 2004年11月

記述言語：英語出版者・発行元：一般社団法人日本物理学会

Structural feature of Eu0.6Sr0.4MnO3 through the magnetic-field-induced insulator-to-metal (IM) transition has been investigated by X-ray powder diffraction in a magnetic field using synchrotron radiation. No superlattice reflections due to the charge and orbital ordering are detected in the insulator phase down to 20 K. Both of the insulator phase and the induced metal phase are proved to be in orthorhombic structure with Pnma space group, and thus a change of the crystal symmetry is not detected on the IM transition. However, the lattice constants abruptly increase and the reflection intensities abruptly change through the transition. These suggest a rotation of MnO6 octahedron in a manner to increase Mn-O-Mn angles. This structural change is consistent with a gain in electron transfer energy in the double exchange mechanism that stabilizes the metallic and ferromagnetic state. © 2004 The Physical Society of Japan.

DOI： 10.1143/JPSJ.73.3059

Magnetic structure of CoO studied by neutron and synchrotron x-ray diffraction 査読

K Tomiyasu, T Inami, N Ikeda

PHYSICAL REVIEW B 70 ( 18 ) 1 - 6 2004年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Below T-N=289 K, the antiferromagnet CoO exhibits magnetic long-range order described by a propagation vector along the trigonal axis, whereas the lattice is distorted monoclinicly along both the tetragonal and the trigonal axes. In order to elucidate this inconsistency, we performed neutron and synchrotron x-ray diffraction experiments on single crystals of CoO, and found a series of magnetic reflections represented by a propagation vector along the tetragonal axis below T-N. These results suggest an altered magnetic structure of CoO, which includes both the trigonal and the tetragonal propagation vectors, has a monoclinic symmetry, and which is in accordance with the distorted lattice symmetry.

DOI： 10.1103/PhysRevB.70.184411

その他リンク： http://orcid.org/0000-0003-2764-0908

Frustration and ordering of iron ions on triangular iron mixed valence system RFe<inf>2</inf>O<inf>4</inf>

N. Ikeda, H. Ohsumi, M. Mizumaki, S. Mori, Y. Horibe, K. Kishimoto

Journal of Magnetism and Magnetic Materials 272-276 2004年5月

We report a resonant X-ray diffraction and a transmission electron microscope observation on triangular layered oxide RFe2O4 (R = Lu and Y). The observed super structure is concluded to be originated from the charge ordering on triangular plane. The origin of the charge ordering is interpreted as the competing interaction of the charges between nearest and next nearest neighbor charges on triangular lattice. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.155

Magnetic field induced phase transition in distorted perovskite Eu <inf>0.6</inf>Sr<inf>0.4</inf>MnO<inf>3</inf>

Shin Nakamura, Shin Nakamura, Susumu Shimomura, Naoshi Ikeda, Masaichiro Mizumaki, Hiroyuki Ohsumi, Shigeki Nimori, Takao Takeuchi, Kikuo Itoh

Journal of Magnetism and Magnetic Materials 272-276 424 - 425 2004年1月

Structural feature of Eu0.6Sr0.4MnO3 through the magnetic field induced insulator-to-metal transition has been investigated by using synchrotron X-ray diffraction in the magnetic field. While keeping the same Pnma symmetry, the lattice constant b jumps at the transition field, which is responsible for magnetoelastic effect. We suggest that the structural change through the transition is a rotation of MnO 6 octahedron in a manner that the Mn-O-Mn angle increases toward 180°. © 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.139

Magnetic behavior of some rare-earth transition-metal perovskite oxide systems

Kenji Yoshii, Akio Nakamura, Masaichiro Mizumaki, Naoshi Ikeda, Jun'ichiro Mizuki

Journal of Rare Earths 22 733 - 738 2004年1月

Relationship between charge stripe order and structural phase transitions in La1.875Ba0.125-xSrxCuO4 査読

H. Kimura, Y. Noda, H. Goka, M. Fujita, K. Yamada, M. Mizumaki, N. Ikeda, H. Ohsumi

Phys. Rev. B 70 ( 13 ) 134512/1 - 134512/8 2004年

Magnetic field induced phase transition in distorted perovskite Eu0.6Sr0.4MnO3 招待

Shin Nakamura, Susumu Shimomura, Naoshi Ikeda

Sprin-8 Research Frontiers 2003 51 - 52 2004年

Structure transition and charge competition on YFe<inf>2</inf>O<inf>4</inf>

Naoshi Ikeda, Ryosuke Mori, Shigeo Mori, Kay Kohn

Ferroelectrics 286 175 - 184 2003年6月

We report the low temperature charge ordered structure and magnetic relaxation in nearly stoichiometric YFe 2 O 4 in which the charge frustration effect is considered to be dominant. The superlattice reflections have revealed the presence of four different phases with a triple, double, quadruple and septuplex charge-superstructure in the temperature range from room temperature to 130 K. The observed successive transitions have been proposed by a previous X-ray powder diffraction study. A slow relaxation of the superstructure was found at 130 K. Time dependence of the magnetic moment was observed at about 240 K to suggest a similar relaxation. © 2003 Taylor & Francis.

DOI： 10.1080/00150190390206356

Critical phenomena in helical magnet beta-MnO2: X-ray magnetic scattering study 査読

H Sato, Y Kawamura, T Ogawa, Y Murakami, H Ohsumi, M Mizumaki, N Ikeda

PHYSICA B-CONDENSED MATTER 329 757 - 758 2003年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

It has been theoretically expected that critical phenomena of helimagnetism is drastically different from those of collinear antiferromagnetism due to the existence of chiral degree of freedom. In order to verify this prediction, we carried out X-ray magnetic scattering measurements on a simplest helimagnet beta-MnO2 using a synchrotron radiation. The critical exponent beta was estimated at 0.25+/-0.05 from the temperature dependence of the scattering intensity. This value is consistent with the predicted value 0.253 for chiral system rather than with 0.346 for collinear system. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02501-2

Synchrotron x-ray diffraction study of a charge stripe order in (formula presented)-doped (formula presented) 査読

M. Fujita, H. Kimura, Y. Noda, K. Yamada, H. Goka, N. Ikeda

Physical Review B - Condensed Matter and Materials Physics 67 ( 14 ) 2003年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

Lattice distortions associated with charge stripe order in (formula presented) hole-doped (formula presented) are studied using synchrotron x-ray diffraction for (formula presented) and (formula presented) The propagation wave-vector and charge order correlation lengths are determined with a high accuracy, revealing that the oblique charge stripes in orthorhombic (formula presented) crystal are more disordered than the aligned stripes in tetragonal (formula presented) crystal. The twofold periodicity of lattice modulations along the c axis is explained by long-range Coulomb interactions between holes on neighboring (formula presented) planes. © 2003 The American Physical Society.

DOI： 10.1103/PhysRevB.67.140503

Review and Prospect of Ferroelectricity and Magnetism in YMn₂O₅ 査読

Yukio Noda, Yoshikazu Fukuda, Hiroyuki Kimura, Isao Kagomiya, S. Matsumoto, Kay Kohn, Takahisa Shobu, Naoshi Ikeda

Journal of the Korean Physical Society 42 S1192 - 1195 2003年4月

Synchrotron x-ray diffraction study of a charge stripe order in 1/8-doped La1.875Ba0.125-xSrxCuO4

H. Kimura, H. Goka, M. Fujita, Y. Noda, K. Yamada, N. Ikeda

Physical Review B - Condensed Matter and Materials Physics 67 ( 14 ) 1405031 - 1405034 2003年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

Lattice distortions associated with charge stripe order in 1/8 hole-doped La1.875Ba0.125-xSrxCuO4 are studied using synchrotron x-ray diffraction for x = 0.05 and x = 0.075. The propagation wave-vector and charge order correlation lengths are determined with a high accuracy, revealing that the oblique charge stripes in orthorhombic x = 0.075 crystal are more disordered than the aligned stripes in tetragonal x = 0.05 crystal. The twofold periodicity of lattice modulations along the c axis is explained by long-range Coulomb interactions between holes on neighboring CuO2 planes.

Synchrotron x-ray diffraction study of a charge stripe order in 1/8 -doped La_1.875Ba_0.125-xSr_xCuO₄

H. Kimura, H. Goka, M. Fujita, Y. Noda, K. Yamada, N. Ikeda

Phys. Rev. B 67 140503(1)-140503(3) 2003年

Study of 2D phase transition of polar organic dye molecules at the air-water interphase by using grazing-incidence x-ray diffraction

N.Kato, I.Hirosawa, M.Sato, N.Ikeda, Y.Uesu

Ferroelectrics 286 921 - 926 2003年

掲載種別：研究論文（国際会議プロシーディングス）

The grazing incidence X-ray diffraction from the 2D polar crystallites of organic dye molecules on an aqueous subphase was measured. The structure of the 2D crystallites shows a dependence on the subphase composition, and this dependence corresponds well to the results obtained from Langmuir-Blodgett films, which consist of the multilayer of the 2D crystallites deposited on the solid planar supports. © 2003 Taylor & Francis.

DOI： 10.1080/00150190390206374

Ground state of NaV₂O₅ under high pressure

K. Ohwada, J. Muraoka, Y. Fujii, H. Nakao, Y. M. Murakami, Y. Noda, N. Ikeda, H. Ohsumi, M. Isobe, Y. Ueda

SPring-8 User Experiment Report 10 14 - 14 2003年

Lattice Distortion at Ferroelectric Transition of YMn₂O₅

I. Kagomiya, S. Mat.sumoto, K. Kohn, Y. Fukuda, T. Shobu, H. Kimura, Y. Noda, N. Ikeda

Ferroelectrics 286 167 - 174 2003年

Improvement of experimental technology at high pressure and low temperature and the observation of superlattice reflections of K₃H(SO₄)₂ at high pressure

Takahisa Shobu, M. Mizumaki, Hiroyuki Ohsumi, Naoshi Ikeda, Yukio Noda

SPring-8 User Experiment Report 11 357 - 357 2003年

Ground state of NaV₂O₅ under high pressure 2

K. Ohwada, Y. Fujii, H. Nakao, Y. M. Murakami, Y. Noda, N. Ikeda, H. Ohsumi, M. Isobe, Y. Ueda

SPring-8 User Experiment Report 11 22 - 22 2003年

Ordered charge asphericity around dysprosium and structural deformation in DyB2C2 査読

H Adachi, H Kawata, M Mizumaki, T Akao, M Sato, N Ikeda, Y Tanaka, H Miwa

PHYSICAL REVIEW LETTERS 89 ( 20 ) 206401 2002年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The oribitally ordered phase of DyB2C2 has been studied by nonresonant x-ray diffraction with high-brilliance synchrotron radiation. From the condition of diffraction, the symmetry property of the charge distribution around dysprosium has been concluded at the quadrupolar level. The quantitative inspection, furthermore, indicates that the observed signals cannot be interpreted as arising only from the 4f electrons of dysprosium responsible for the ordering; instead, the experiment can be described rather well by considering a distortion of the metaloid network concomitant with the ordering.

DOI： 10.1103/PhysRevLett.89.206401

Symmetry breaking in the metal-insulator transition of BaVS<inf>3</inf>

T. Inami, K. Ohwada, H. Kimura, M. Watanabe, Y. Noda, H. Nakamura, T. Yamasaki, T. Yamasaki, M. Shiga, N. Ikeda, Y. Murakami, Y. Murakami

Physical Review B - Condensed Matter and Materials Physics 66 731081 - 731084 2002年8月

It has been believed for a long time that the metal-to-insulator (MI) transition of BaVS3 is not accompanied by any spatial order of the spin and lattice. We have carried out x-ray-diffraction measurements of BaVS3 single crystals using a laboratory x-ray source as well as synchrotron radiation, and found that superlattice reflections which double the lattice constant c exist below the transition temperature. The most probable space group at the low-temperature insulator phase contains two inequivalent vanadium sites, and thus a charge disproportionation of the vanadium ions is considered the main cause of the MI transition.

DOI： 10.1103/PhysRevB.66.073108

X-ray absorption spectroscopy in NaCo2O4, LaCoO3 and SrCoO3 査読

T Matsushita, M Mizumaki, N Ikeda, M Nakazawa, A Agui, Y Saitoh, T Nakatani, A Yoshigoe, S Nakamura

SURFACE REVIEW AND LETTERS 9 ( 2 ) 1327 - 1331 2002年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WORLD SCIENTIFIC PUBL CO PTE LTD

We have performed Co 2p X-ray absorption spectroscopy (XAS) on a mixed valence hexagonal layered system NaCo2O4, which shows large thermopower and metallic conductivity. We also measured XAS for SrCoO3 and LaCoO3 as examples of typical Co ionic states. The Co ions of the last two materials are octahedrally surrounded by oxygen atoms. A Co atom in NaCo2O4 also has octahedral coordination with oxygen atoms but it is distorted slightly. The Co ions in SrCoO3 and LaCoO3 are in the d(5) and d(6) configuration respectively. The spectrum of NaCo2O4 resembles that of LaCoO3 rather than that of SrCoO3; the Co ions in NaCo2O4 can be regarded as the d(6) configuration. Also, we have tried to calculate the XAS spectra by using the charge-transfer multiplet model (CT-M). Although we could not find out the best-fitting parameters, the results suggested the itinerancy of the Co 3d states.

Dielectric and structure properties of charge competing system YFe 2O4

Naoshi Ikeda, Ryosuke Mori, Kay Kohn, Masaichiro Mizumaki, Takahiro Akao

Ferroelectrics 272 309 - 314 2002年1月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Taylor and Francis Inc.

YFe2O4-δ ( δ &lt
0.005), which is a member of charge-frustrated system RFe 2 O 4 was synthesized and investigated by the low-temperature synchrotron powder X-ray diffraction. The structure between 225K and 250K is the same with the three-dimensional charge ordered state of LuFe 2 O 4 . Below the charge ordering temperature, at least five different phase transitions were detected. Since the balance of competing interaction between ionic charge essentially dominates the presence of multi phases in frustrated system, the low oxygen deficiency in YFe2O 4-δ is considered as the origin of the multi phases in low temperature. © 2002 Taylor &amp
Francis.

DOI： 10.1080/713716255

Accurate Measurement of Lattice Parameters on YMn₂O₅ 査読

Isao Kagomiya, Naoshi Ikeda, Yukio Noda, S. Matsumoto, Yoshikazu Fukuda, Hiroyuki Kimura, Kay Kohn

SPring-8 User Experiment Report 7 26 - 26 2001年4月

X-ray Diffraction Study on Ca_{2 x}Y_2-xCu₅O₁₀ 査読

H. Yamaguchi, Hiroyuki Kimura, Masashi Watanabe, Yoshikazu Fukuda, Naoshi Ikeda, Yukio Noda

SPring-8 User Experiment Report 6 18 - 18 2001年4月

Single Crystal Analysis of High-Pressure Phase of Solid Oxygen 査読

Y. Akahama, E. Uemura, M. Harada, H. Kawamura, Masashi Watanabe, Yukio Noda, Naoshi Ikeda, Osamu Shimomura

SPring-8 User Experiment Report 7 22 - 22 2001年4月

Development of BL02B1 査読

Naoshi Ikeda, Y. Yoneda, Takahisa Shobu, Hiroyuki Kimura, Masashi Watanabe, Yoshikazu Fukuda, Isao Kagomiya, S. Matsumoto, Yukio Noda

SPring-8 User Experiment Report 6 23 - 23 2001年4月

"Devil's staircase"-type phase transition in NaV2O5 under high pressure 査読

Ohwada K, Fujii Y, Takesue N, Isobe M, Ueda Y, Nakao H, Wakabayashi Y, Murakami Y, Ito K, Amemiya Y, Fujihisa H, Aoki K, Shobu T, Noda Y, Ikeda N

PHYSICAL REVIEW LETTERS 87 ( 8 ) 2001年

Charge Frustration and Dielectric Dispersion in LuFe2O4

Ikeda Naoshi, Kohn Kay, Myouga Nobuyuki, Takahashi Eri, Kitôh Hijiri, Takekawa Shunji

Journal of the Physical Society of Japan 69 ( 5 ) 1526 - 1532 2000年5月

記述言語：英語出版者・発行元：一般社団法人日本物理学会

We report the dielectric anomaries at the phase transitions ofLu(Fe2+ Fe3+)O4, which is considered as a charge andspin frustrated system.Dielectric constant shows a hump, just above the transition from thehigh temperature two-dimensional to the low temperaturethree-dimensional charge ordering. A few glassy behaviors wereobserved at this transition. The presence of spontaneous polarizationin the low temperature phase was confirmed by the measurement ofpyroelectricity. A step-wise increase of the dielectric constant withincreasing temperature was observed between 150 K and 250 K as inother RFe2O4.These phenomena are explained by the presence of the polar domainswith the ordering of Fe2+ and Fe3+ and the motions of theantiphase boundaries between them.

DOI： 10.1143/JPSJ.69.1526

X-ray diffuse scattering study on charge-localized states

S. Shimomura, T. Tonegawa, K. Tajima, N. Wakabayashi, N. Ikeda, T. Shobu, Y. Noda, Y. Tomioka, Y. Tokura

Physical Review B - Condensed Matter and Materials Physics 62 ( 6 ) 3875 - 3878 2000年

掲載種別：研究論文（学術雑誌）

X-ray scattering measurements on (Formula presented) have revealed the existence of diffuse scattering above the charge and orbital ordering transition temperature (Formula presented) The diffuse scattering has local intensity maxima at incommensurate positions (Formula presented) With decreasing temperature, (Formula presented) increases from about 0.4, and it discontinuously changes to 0.5 at (Formula presented) Characteristic patterns of diffuse intensity distributions can be qualitatively interpreted by calculations based on distortion fields associated with the Jahn-Teller effect. The observed patterns are similar to those observed above the ferromagnetic insulator-metal transition temperature in (Formula presented) reported previously. © 2000 The American Physical Society.

DOI： 10.1103/PhysRevB.62.3875

Synchrotron observation of the charge ordering and spontaneous polarization in LuFe<inf>2</inf>O<inf>4</inf>

Naoshi Ikeda, Masahiko Tanaka, Hijiri Kitô, Satoshi Sasaki, Yasusada Yamada

Ferroelectrics 222 ( 1-4 ) 227 - 235 1999年

掲載種別：研究論文（学術雑誌）

We report a synchrotron orbital radiation study of a charge ordering in a triangular mixed valence system LuFe2O4. Using the X-ray anomalous dispersion method near the iron K-shell absorption edge, we confirmed a superstructure of Fe2+ and Fe3+ on the triangular lattice with a configuration of a √3 × √3 × 2 structure. This charge structure shows a spontaneous polarization. The existence of two dimensional charge ordering above 330K was deduced from the temperature dependence of the energy dispersion for the superlattice reflection.

DOI： 10.1080/00150199908014820

Charge ordering in La1-xSrxMnO3 (x similar to 0.12) 査読

Inami T, Ikeda N, Murakami Y, Koyama I, Wakabayashi Y, Yamada Y

Japanese Journal of Applied Physics Part 1-Regular Papers Brief Communications & Review Papers 38 212 - 214 1999年

Charge ordering of LuFe<inf>2</inf>O<inf>4</inf> observed by an anomalous X-ray dispersion

Naoshi Ikeda, Shinichiro Nohdo, Yasusada Yamada, Eri Takahashi, Kay Kohn

Journal of the Korean Physical Society 32 ( SUPPL. 1 ) 1998年2月

掲載種別：研究論文（学術雑誌）

We observed a superlattice reflection for triangular layered oxide LuFe2O4 by using anomalous X-ray dispersion with synchrotron radiation source. We found that superlattice spot (1/3, 1/3, 4.5) shows a large intensity variation upon a slight change of incident X-ray energy (wave length) from 7.114 keV (1.7437 Å) to 7.1448 keV (1.7353 Å) across the Fe absorption edge. This phenomenon is explained by superlattice structure of Fe2+ and Fe3+ on triangular lattice. The existence of the superlattice structure due to the charge ordering of iron ions on triangular lattice indicates that LuFe2O4 possesses local spontaneous polarization.

Valence fluctuation and polarization fluctuation in LuFe<inf>2</inf>O<inf>4</inf>

Yasusada Yamada, Naoshi Ikeda

Journal of the Korean Physical Society 32 ( SUPPL. 1 ) 1998年2月

掲載種別：研究論文（学術雑誌）

The anomalous dielectric behavior of mixed valence system LuFe2O4 is investigated. It has been shown that LuFe2O4 undergoes successive phase transitions associated with ordering of charge configuration of Fe ion following the sequence of disorder → 2D-CDW (charge density wave) → 3D-CDW state. The stable 3D-CDW phase is characterized by a long period incommensurate antiferroelectric phase. The anomalously high dielectric constant at lower temperature as well as its frequency dependence is discussed in connection with the motion of the antiphase domain boundaries.

Dielectric dispersion and charge ordering of LuFe<inf>2</inf>O<inf>4</inf>

Eri Takahashi, Kay Kohn, Naoshi Ikeda

Journal of the Korean Physical Society 32 ( SUPPL. 1 ) 1998年2月

掲載種別：研究論文（学術雑誌）

A layer-structure oxide LuFe2O4 shows dielectric dispersions in two temperature regions below and above the transition between two- and three-dimensional charge orderings proposed by a diffraction study. The origin of the dispersions are considered to be related with electron hopping between Fe2+ and Fe3+ ions ordered or disordered on triangular lattices characteristic of this oxide.

Incommensurate Charge Ordering in Charge-Frustrated LuFe<inf>2</inf>O<inf>4</inf> System

Yasusada Yamada, Shinichiro Nohdo, Naoshi Ikeda

Journal of the Physical Society of Japan 66 ( 12 ) 3733 - 3736 1997年

掲載種別：研究論文（学術雑誌）

The charge ordering process of a mixed valence LuFe2O4 system has been studied, focusing attention on the frustration effect associated with the charge configuration, ft is revealed that the system undergoes successive phase transitions following the sequence of disorder→2D CDW→3D CDW. In the 2D-CDW state, the charge density wave defined by the wave vector (1/3,1/3), is formed in the hexagonal layer. On the nodal lines of the CDW, the charge order is still undetermined due to the charge frustration. From a dielectric viewpoint, this phase is viewed as random stacking of 2D ferroelectric layers. In the 3D-CDW state, antiphase stacking of the 2D ordered layer develops. At the same time, the in-plane charge order exhibits a doubly modulated long-period structure. From a dielectric viewpoint, this phase is characterized by an incommensurate antiferroelectric phase. Relevance of the charge ordering mechanism to the observed anomalously large dielectric constant in LuFe2O4 is discussed. © 1997, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.66.3733

Dipole glass behavior of RFe<inf>2</inf>O<inf>4</inf>

N. Ikeda, K. Odaka, E. Takahashi, K. Kohn, K. Siratori

Ferroelectrics 190 ( 1-4 ) 191 - 196 1997年

掲載種別：研究論文（学術雑誌）

We report low frequency dielectric dispersions of ErFe2O4 in which equal numbers of Fe2+ and Fe3+ ions occupy the sites on a triangular lattice. The first dispersion observed between 200 K and 300 K is explained qualitatively on a model that spontaneous polarization is present in the crystal below the Verwey transition. The second dispersion at higher temperatures is characterized by a few glass-like features. It was interpreted by successive freezing of the local dipole moments accompanied by short-range ordering of Fe2+ and Fe3+ ions.

DOI： 10.1080/00150199708014115

Incommensurate charge ordering in mixed valence system LuFe<inf>2</inf>O<inf>4</inf>

Naoshi Ikeda, Yasusada Yamada, Shinichiro Nohdo, Toshiya Inami, Susumu Katano

Physica B: Condensed Matter 241-243 820 - 822 1997年

掲載種別：研究論文（学術雑誌）

Charge ordering of a mixed valence system LuFe2O4 has been studied by neutron scattering technique, focusing attention on the charge frustration effect on triangular lattice. It is revealed that the system undergoes successive phase transitions following the sequence of disorder → two-dimensional charge density wave state (2D-CDW) → three-dimensional charge density wave state (3D-CDW). In 2D-CDW state, the charge density wave defined by the wave vector (1/3 1/3) is formed in the hexagonal layer, © 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(97)00728-X

Charge ordering in low-doping rate A<inf>1-x</inf>B<inf>x</inf>MnO<inf>3</inf> (A: La, Pr; B: Sr, Ca)

T. Inami, O. Hino, S. Nohdo, R. Kanao, N. Ikeda, Y. Yamada, S. Katano

Physica B: Condensed Matter 241-243 433 - 435 1997年

掲載種別：研究論文（学術雑誌）

We have found charge ordering in perovskite-type manganese oxides at low-carrier-doping region in neutron diffraction experiments. In La1-xSrxMnO3 (x = 0.1 and 0.15), we observed superlattice reflections at commensurate positions and the onset temperature Tp of the superlattice structure coincides with the low-temperature metal-toinsulator transition point. Pr1-xCaxMnO3 compounds are also studied at the stoichiometric concentration of x = 0.25. We observed diffuse satellite peaks indicating the existence of new charge-ordered state at this concentration. © 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(97)00611-X

Anisotropy of Dielectric Dispersion in ErFe<inf>2</inf>O<inf>4</inf> Single Crystal

Naoshi Ikeda, Kay Kohn, Hijiri Kito, Jun Akimitsu, Kiiti Siratori

Journal of the Physical Society of Japan 64 ( 4 ) 1371 - 1377 1995年4月

掲載種別：研究論文（学術雑誌）

Dielectric dispersion was observed in a single crystal with the composition of ErFe2O3.95 below magnetic transition temperature. It is characterized by a large dielectric constant of the order of 104, and a Debye-type frequency dependence like in the poly crystalline samples of the same substance which we reported in a previous paper. Large anisotropy exists in the strength εs − ε∞ and the characteristic relaxation frequency of the dispersion. The strength is higher within the c-plane than along the c-axis, while the characteristic frequency is much larger along the c-axis than within the c-plane. The dielectric dispersion in the polycrystalline sample cannot be explained by a simple average of the single crystal results. The observed dispersion is qualitatively discussed with a model of domain wall motion on an assumption that ErFe2O4 is a polar crystal. © 1995, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.64.1371

Magnetic Relaxation in Diluted Triangular Antiferromagnet LuFeMgO<inf>4</inf>

Naoshi Ikeda, Kay Kohn, Etsuko Himoto, Midori Tanaka

Journal of the Physical Society of Japan 64 ( 11 ) 4371 - 4377 1995年

掲載種別：研究論文（学術雑誌）

We observed a few magnetic relaxation phenomena in a LuFeMgO4single crystal, that is, the difference in the magnetization between field-cooled and zero-field-cooled specimens, the appearance of thermoremanent magnetization, and the frequency dependence of the cusp temperature of AC susceptibility. The observed relaxation was interpreted in terms of thermal fluctuations and freezing of the magnetic clusters which are supposed to exist in this substance. © 1995, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.64.4371

Possibility of magnetoelectric effect in antiferromagnetic rfe2o4

Naoshi Ikeda, Kazuhiro Saito, Kay Kohn

Ferroelectrics 161 ( 1 ) 111 - 115 1994年1月

掲載種別：研究論文（学術雑誌）

We report the magnetoelectric effect of a polycrystalline sample of a triangular Ising antiferromagnet ErFe2O4-8, in which the existence of short range charge ordering was inferred from the neutron and dielectric studies. The sign of the magnetoelectric signal was reversed at 77 K, when the electric or magnetic field was applied in the opposite directions during cooling the specimen down to 77 K. The sign of the signal was independent of the direction of the static bias magnetic field in the range above 150 K. The signal was maximum at 183 K. We suggest a relation between the origin of the magnetoelectric effect and the dielectric relaxation due to an electron hopping between Fe3+ and Fe2+ sites. © 1994, Taylor & Francis Group, LLC. All rights reserved.

DOI： 10.1080/00150199408213359

Dielectric Relaxation and Hopping of Electrons in ErFe204

Naoshi Ikeda, Kay Kohn, Hijiri Kito, Jun Akimitsu, Kiiti Siratori

Journal of the Physical Society of Japan 63 ( 12 ) 4556 - 4564 1994年

掲載種別：研究論文（学術雑誌）

We report the frequency and the temperature dependence of the dielectric constant of polycrystalline ErFe2O4-δ with different degrees of oxygen deficiency S. a large dielectric relaxation, with the order of magnitude of 104 and nearly of the Debye type, is observed in the magnetically ordered states within the temperature and frequency ranges of 150 k to 290 K and 1 kHz to 3 MHz, respectively. The dispersion is larger in the sample with more oxygen deficiency. From the temperature dependence of the characteristic frequency, we conclude that the elementary process of the dispersion is related to electron hopping between Fe2+ and Fe3+ ions. a large value of the dielectric constant is consistent with the existence of spontaneous polarization in the magnetic phases of this oxide. We propose that the motion of the polarization domain boundaries is a determining factor of low-frequency dielectric constant. © 1994, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.63.4556

Cd substitution effect on the superconducting transition temperature in RE<inf>1-x</inf>Cd<inf>x</inf>Ba<inf>2</inf>Cu<inf>3</inf>O<inf>y</inf>

Naoshi Ikeda, Sadao Higuchi, Kay Kohn

Phase Transitions 41 ( 1-4 ) 209 - 215 1993年1月

掲載種別：研究論文（学術雑誌）

We report the change of the superconducting transition temperature Tc with the substitution of rare earth with cadmium in the RE1-xCdxBa2Cu3Oy system, where RE is Nd, Eu, Gd, Dy and Y. The decrease of Tc with the amount of Cd was found to be closely related to the radius of the RE3+ ion. © 1993, Taylor & Francis Group, LLC. All rights reserved.

DOI： 10.1080/01411599308207781

A simple alternating current magnetometer for high temperature superconductivity study

Naoshi Ikeda, Kay Kohn

Phase Transitions 42 ( 1-2 ) 7 - 14 1993年1月

Spin-glass behavior in amorphous BiFeO3 査読

Shin Nakamura, Susumu Soeya, Naoshi Ikeda, Midori Tanaka

Journal of Applied Physics 74 ( 9 ) 5652 - 5657 1993年

記述言語：英語掲載種別：研究論文（学術雑誌）

Short-range antiferromagnetic (speromagnetic) behavior was observed for amorphous BiFeO3 by static magnetic measurements, ac susceptibility (χac) measurement, and 57Fe Mössbauer spectra measurements. The magnetic behavior is classified into three temperature ranges: (i) paramagnet for T≳220 K
(ii) local clustering of spins for 20 K&lt
T&lt
220 K
and (iii) speromagnet in which all spins are frozen into random directions for T&lt
20 K. In the spin freezing state the magnetization shows irreversibility and the χac-T curve has a cusp. The variation of the spin freezing temperature against measuring magnetic field and measuring frequency indicate that the speromagnetic order is very similar to that of spin glass.

DOI： 10.1063/1.354179

Effect of Pr substitution on superconductivity in (PrxY1−x)Ba2Cu4O8

Nobuyoshi Yamada, Zhen Guo, Naoshi Ikeda, Kay Kohn, Takeo Iri, Ken Ichiro Gondaira

Physica C: Superconductivity 185-189 809 - 810 1991年12月

A Simple Alternating Current Magnetometer of the Automatic Balancing Type

Ikeda Naoshi, Kohn Kay

Jpn J Appl Phys 29 ( Part 1, No. 1 ) 208 - 209 1990年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：社団法人応用物理学会

An improvement of a Hartshorn type alternating current magnetometer is reported. The use of a dual channel oscillator, a two-phase lock-in amplifier and a personal computer enabled us to obtain a simple feedback system for automatic balancing of the bridge. The resolution of this system is about $3\times 10^{-7}$ emu of magnetic moment or higher at the field of 0.8 Oe in amplitude and 159 Hz in frequency.

DOI： 10.1143/jjap.29.208

Suppression of superconductivity by lanthanum substitution in the Bi4Ca3Sr3Cu4Oy system

N. Ikeda, K. Kohn, E.V. Sampathkumaran, R. Vijayaraghavan

Solid State Communications 68 ( 1 ) 51 - 55 1988年10月

Influence of chemical substituents on the superconductivity of the system Bi4Ca3Sr3Cu4Oy

E V Sampathkumaran, N Ikeda, K Kohn, R Vijayaraghavan

Journal of Physics F: Metal Physics 18 ( 8 ) L163 - L167 1988年8月

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