研究者詳細 - 小山　佳一

論文 - 小山　佳一

分割表示 496 件中 241 - 260 件目／全件表示 >>

Makoto Yoshida, Yumiko Kitano, Yuji Inagaki, Takahiro Sakurai, Motoi Kimata, Susumu Okubo, Hitoshi Ohta, Keiichi Koyama, Mitsuhiro Motokawa, Takayuki Asano, Yoshitami Ajiro . Observation of direct transitions in the ferromagnetic and antiferromagnetic dimer system (CH3)(2)NH2CUCl3 by high-field ESR . JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN76 ( 11 ) 2007年11月査読

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

High-field electron spin resonance (ESR) measurements of single crystals of (CH3)(2)NH2CuCl3 (DMACuCl(3)) have been performed in the frequency range of 50 to 550 GHz in the paramagnetic region. In addition to the electron paramagnetic resonance, we have observed four ESR modes omega(1), omega(2), omega(3), and omega(4). The modes omega(2) and omega(3) have a frequency gap of 325 GHz (15.6 K), while the mode omega(1) has a gap of 420 GHz (20 K) at 0 T. The modes omega(2) and omega(3) are attributed to the transitions between the singlet and the triplet of the antiferromagnetic (AF) dimer. We found that the large spin-gap for the AF dimer still remains at the critical field B-c2 = 3.5 T determined by magnetization and specific heat measurements.

DOI： 10.1143/JPSJ.76.113704

Web of Science

K. Hachitani, H. Amanuma, H. Fukazawa, Y. Kohori, I. Watanabe, K. Koyama, K. Kumagai, C. Sekine, I. Shirotani . Sm-based Filled Skutterudite Phosphides SmT<inf>4</inf> P<inf>12</inf> (T = Fe, Ru, Os) Studied by <sup>31</sup>P-NMR and μSR . Journal of Physics and Chemistry of Solids68 ( 11 ) 2080 - 2083 2007年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

The Sm-based filled skutterudite phosphides SmT4 P12 (T = Fe, Ru, Os) have been studied by 31P-NMR (nuclear magnetic resonance) and μSR (muon spin relaxation). The ferromagnetic order and the heavy fermion behavior in SmFe4 P12 and the antiferromagnetic order in SmOs4 P12 were confirmed by 31P-NMR and μSR. In SmRu4 P12, a successive anomaly around the metal-insulator transition temperature and around the Néel temperature was observed by 31P-NMR in high applied magnetic fields. The μSR results of SmRu4 P12 indicate the magnetic order below the metal-insulator transition temperature, which supports the existence of the octupolar order in SmRu4 P12. © 2007.

DOI： 10.1016/j.jpcs.2007.08.033

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E. A. Tereshina, A. V. Andreev, K. Koyama, Y. Shiokawa, I. Satoh, K. Watanabe . Magnetic anisotropy and spin reorientation in U2Co15Si2 . JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS316 ( 2 ) E515 - E518 2007年9月査読

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

Field and temperature dependencies of the magnetization measured along the principal axes of a U2Co15Si2 single crystal show that this compound is a ferromagnet with a spontaneous magnetic moment of 14.8 mu(B) per formula unit (at 4.2 K), located in the basal plane of the hexagonal crystal structure. A strong easy-plane magnetic anisotropy (K-1 = -0.97 MJ m(-3) at 4.2 K) is attributed to the U sublattice because Lu2Co15Si2 exhibits easy-axis anisotropy with K-1 = 0.42 MJ m(-3). The easy-plane anisotropy of U2Co15Si2 transforms to a cone of easy axes above 270 K. The magnetization vector approaches the c-axis at 350 K, and the compound has easy c-axis anisotropy up to the Curie temperature T-C = 601 K. (C) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.jmmm.2007.03.006

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A. V. Andreev, K. Koyama, N. V. Mushnikov, V. Sechovsky, Y. Shiokawa, I. Satoh, K. Watanabe . Interplay between effects of external pressure and dilution of the U sublattice in UCoAl-based materials . JOURNAL OF ALLOYS AND COMPOUNDS441 ( 1-2 ) 33 - 38 2007年8月査読

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

Substitution of Y for U in the itinerant 5f-electron metamagnet, UCoAl, transforms the system to a ferromagnetic state. Application of external hydrostatic pressure above 0.3 GPa suppresses the ferromagnetism and restores the "UCoAl-type" metamagnetism back. However, the metamagnetic transition becomes of the second order instead of the first order one in parent UCoAl. This is attributed to enhancement of fluctuations of the U magnetic moment upon dilution of the U sublattice. (C) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2006.09.111

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Tetsuya Onogi, Keiichi Koyama, Kazuo Watanabe . Magnetic properties of MnBi in high magnetic fields and high temperature . JOURNAL OF THE JAPAN INSTITUTE OF METALS71 ( 6 ) 489 - 493 2007年6月査読

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：JAPAN INST METALS

Magnetization measurements of polycrystalline MnBi were carried out in magnetic fields up to 10 T and in the temperature range from 300 to 773 K, in order to clarify the magnetic properties under high magnetic fields and high temperature. The magnetic phase transition temperature (T-c) at a zero magnetic field is 633 K, which almost linearly increases by 2.3 KT-1 with increasing fields up to 10 T. Furthermore, a metamagnetic transition was observed just above T, indicating that the phase transition is first order. The magnetic entropy change is estimated to be 14 J kg(-1) K-1 for 2 T at T-c using Clausius-Clapayron's equation, which is almost constant for magnetic fields up to 10 T.

DOI： 10.2320/jinstmet.71.489

Web of Science

M. Matsukawa, Y. Yamato, T. Kumagai, A. Tamura, R. Suryanarayanan, S. Nimori, M. Apostu, A. Revcolevschi, K. Koyama, N. Kobayashi . Steplike lattice deformation of single crystalline (La0.4Pr0.6)(1.2)Sr1.8Mn2O7 bilayered manganite . PHYSICAL REVIEW LETTERS98 ( 26 ) 2007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：AMERICAN PHYSICAL SOC

We report a steplike lattice transformation of single crystalline (La0.4Pr0.6)(1.2)Sr1.8Mn2O7 bilayered manganite accompanied by both magnetization and magnetoresistive jumps, and examine the ultrasharp nature of the field-induced first-order transition from a paramagnetic insulator to a ferromagnetic metal phase accompanied by a huge decrease in resistance. Our findings support that the abrupt magnetostriction is closely related to an orbital frustration existing in the inhomogeneous paramagnetic insulating phase rather than a martensitic scenario between competing two phases.

DOI： 10.1103/PhysRevLett.98.267204

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T. Sakon, S. Saito, K. Koyama, S. Awaji, I. Sato, T. Nojima, K. Watanabe, N. K. Sato . Experimental investigation of giant magnetocrystalline anisotropy of UGe2 . PHYSICA SCRIPTA75 ( 4 ) 546 - 550 2007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：IOP PUBLISHING LTD

UGe2 is a ferromagnetic heavy-fermion (HF) superconductor, which provides superconductivity under pressure in the range of 1.0 to 1.5 GPa. In this paper, we conducted detailed magnetization experiments up to 27 T and at atmospheric pressure. Magnetization along the a-axis indicates typical ferromagnetic property. On the other hand, magnetization along the b-axis is quite a bit smaller than that of the easy a-axis. The magnetocrystalline anisotropy constant is the same as the rare earth ferromagnet Nd2Fe17, which indicates that UGe2 is a highly anisotropic ferromagnet.

DOI： 10.1088/0031-8949/75/4/030

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S. V. Demishev, A. V. Semeno, A. A. Pronin, N. E. Sluchanko, N. A. Samarin, H. Ohta, S. Okubo, M. Kimata, K. Koyama, M. Motokawa, A. V. Kuznetsov . Quantum criticality and collective effects in low-dimensional magnet CuGeO3 : Fe probed by high frequency EPR . JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM20 ( 2 ) 105 - 108 2007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：SPRINGER

For CuGeO3 single crystals doped with 1% of Fe, the quantum critical behavior in a wide temperature range 1-40 K is reported. The critical exponents for susceptibility along different crystallographic axes are determined: alpha = 0.34 (B parallel to a and B parallel to c) and alpha = 0.31 (B parallel to b). The description of the temperature dependencies of the line width and g-factor could be obtained in the Oshikawa-Affleck theory assuming that staggered component of the magnetic moment is located predominantly along b-axis. Possible arguments favoring the competition between effects of the staggered field and antiferromagnetic ordering are provided.

DOI： 10.1007/s10948-006-0214-3

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M. Yoshida, Y. Kitano, Y. Inagaki, T. Sakurai, M. Kimata, S. Okubo, H. Ohta, K. Koyama, M. Motokawa, T. Asano, and Y. Ajiro . Observation of direct transitions in the ferromagnetic and antiferromagnetic dimmer system (CH3)2NH2CuCl3 by high-field ESR . J. Phys. Soc. Jpn76 113704 2007年1月査読

M. Matsukawa, A. Tamura, S. Nimori, R. Suryanarayanan, T. Kumagai, Y. Nakanishi, M. Apostu, A. Revcolevschi, K. Koyama, N. Kobayashi . Anomalous pressure effect on the remanent lattice striction of a (La,Pr)(1.2)Sr1.8Mn2O7 bilayered manganite single crystal . PHYSICAL REVIEW B75 ( 1 ) 2007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：AMERICAN PHYSICAL SOC

We have studied the pressure effect on magnetostriction, both in the ab plane and along the c axis of a (La, Pr)(1.2)Sr1.8Mn2O7 bilayered manganite single crystal over the temperature region where the field-induced ferromagnetic metal (FMM) transition takes place. For comparison, we have also examined the pressure dependence of magnetization curves at the corresponding temperatures. The applied pressure reduces the critical field of the FMM transition and it enhances the remanent magnetostriction. An anomalous pressure effect on the remanent lattice relaxation is observed and is similar to the pressure effect on the remanent magnetization along the c axis. These findings are understood from the viewpoint that the double-exchange interaction-driven FMM state is strengthened by the application of pressure.

DOI： 10.1103/PhysRevB.75.014427

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Evgeniya A. Tereshina, Hajime Yoshida, Alexander V. Andreev, Irina S. Tereshina, Keiichi Koyama, Takeshi Kanomata . Magnetism of a Lu<inf>2</inf>Fe<inf>17</inf>H single crystal under pressure . Journal of the Physical Society of Japan76 82 - 83 2007年1月査読

記述言語：英語掲載種別：研究論文（学術雑誌）

Lu2Fe17 is a ferromagnet below TC∼140 K and antiferromagnet up to TN=275 K. Hydrogen absorption leads to a stabilization of the ferromagnetism over the whole range of magnetic order and to an increase of the ordering temperature up to TC=354 K in Lu 2Fe17H. The external pressure compensates the lattice expansion upon hydrogenation, and a reentrance of antiferromagnetism is observed. © 2007 The Physical Society of Japan.

DOI： 10.1143/JPSJS.76SA.82

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M. Kimata, Y. Oshima, H. Ohta, K. Koyama, M. Motokawa, H. M. Yamamoto, R. Kato . Low-temperature Fermi surface of the organic conductor β″ -(BEDT-TTF) (TCNQ)(1-x) (F1-TCNQ)x (x=0,0.05) from magnetooptical measurements . Physical Review B - Condensed Matter and Materials Physics75 ( 4 ) 2007年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

Magnetooptical measurements have been performed on the organic conductor β″ -(BEDT-TTF)(TCNQ) (x=0 salt), and a related compound, β″ -(BEDT-TTF)(TCNQ) 0.95 (F1-TCNQ) 0.05 (x=0.05 salt), to investigate their low-temperature Fermi surfaces (FSs). Although the room-temperature FS of both salts can be considered the same, our results indicate that the low-temperature FSs are completely different from each other. In the x=0 salt, the low-temperature FS consists of two very anisotropic quasi-two-dimensional (Q2D) FSs. Cross-sectional areas of anisotropic Q2D-FSs are very small, and correspond to 1-2 % of the first Brillouin zone at room temperature. On the other hand, in the x=0.05 salt, only a pair of quasi-one-dimensional FSs exist at low temperature. Compared with the band calculation of x=0 salt, this Q1D-FS originates from the BEDT-TTF conducting layers. This result indicates that the two hump-like anomalies in the temperature dependence of resistivity at 80 and 20 K, which are observed only in the x=0 salt, are related to the nesting of BEDT-TTF Q1D-FS. Hence, it is considered that anisotropic Q2D-FS pockets observed in the x=0 salt are generated by the imperfect nesting of Q1D-FS, and the density wave state may be formed in the x=0 salt at low temperatures. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevB.75.045126

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Alexander V. Andreev, Keiichi Koyama, Nikolai V. Mushnikov, Vladimir Sechovsky, Yoshinobu Shiokawa, Isamu Satoh, Kazuo Watanabe . Transition from ferromagnetism to metamagnetism under pressure in a uo.94yo.o6coal single crystal . Journal of the Physical Society of Japan76 43 - 46 2007年1月査読

記述言語：英語掲載種別：研究論文（学術雑誌）

Substitution of Y for U in the itinerant 5f-electron metamagnet UCoAl transforms the system to a ferromagnetic ground state. Application of external hydrostatic pressure above 0.3 GPa suppresses the ferromagnetism and restores the "UCoAl-type" metamagnetism. However, the metamagnetic transition becomes of the second-order type instead of the first-order one for the parent UCoAl. © 2007 The Physical Society of Japan.

DOI： 10.1143/JPSJS.76SA.43

Web of Science

Scopus

K. Koyama, S. Miura, H. Okada, T. Shigeoka, K. Watanabe . Magnetic entropy changes of SmMn2Ge2 under high pressure . Mater. Trans.48 451 - 454 2007年査読

K. Hachitani, H. Amanuma, H. Fukazawa, Y. Kohori I. Watanabe, K. Koyama, K. Kumagai, C. Sekine and I. Shirotani . Sm-based filled Skutterudite phosphides SmT4P12 (T=Fe, Ru, Os) studied by 31P-NMR and μSR . J. Phys. Chem. Solid68 2080 - 2083 2007年査読

M. Matsukawa, Y. Yamato, T. Kumagai, A. Tamura, R. Suryanarayanan, S. Nimori, M. Apostu, A. Recolevschi, K. Koyama, and N. Kobayashi . Steplike lattice deformation of single crystalline (La0.4Pr0.6)1.2Sr1.8Mn2O7 bilayered Manganite . Phys. Rev. Lett.98 267204 2007年査読

E.A. Tereshina, A.V. Andreev, K. Koyama, Y. Shiokawa, I. Satoh, and K. Watanabe . Magnetic anisotropy and spin reorientation U2Co15Si2 . J. Magn. Magn. Mater316 e515 - e518 2007年査読

A.V. Andreev, E.A. Tereshina, E. Santava, K. Koyama, Y. Homma, I. Satoh, T. Yamamura, Y. Shiokawa, K. Watanabe . Crystal structure and magnetic properties of U2Co17-xSix single crystals . J. Magn. Magn. Mater.310 e598 - e600 2007年査読

A. Himori, M. Tanaka, K. Koyama, K. Watanabe and T. Shigeoka . Magnetic behavior of TbRh2Si2 single crystal . J. Magn. Magn. Mater.310 1770 - 1772 2007年査読

T. Sakon, S. Saito, K. Koyama, S. Awaji, I. Sato, T. Nojima, K. Watanabe and N.K. Sato . Experimental investigation of giant magnetocrystaline anisotropy of UGe2 . Phys. Scr.75 546 - 550 2007年査読

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論文 - 小山　佳一