研究者詳細 - 池田　直

論文 - 池田　直

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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).

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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

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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.

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