研究者詳細 - 池田　直

論文 - 池田　直

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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

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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

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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

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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.

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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

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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

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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.

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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

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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

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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

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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

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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

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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

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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

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