研究者詳細 - 池田　直

論文 - 池田　直

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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

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