研究者詳細 - 小山　佳一

論文 - 小山　佳一

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T Sakon, H Nojiri, K Koyama, T Asano, Y Ajiro, M Motokawa . Electron spin resonance study of Cu benzoate using a He-3-He-4 dilution refrigerator . JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN70 ( 8 ) 2259 - 2262 2001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

An electron spin resonance (ESR) measurement system for use at ultralow temperatures using a He-3-He-4 dilution refrigerator has been developed. As the first experiment. the ESR was measured on a quantum spin chain Cu benzoate clown to 160 ml. in which a field-induced gap was recently found.((4)) The evaluation of a new ESR mode. the so-called breather mode, was found at the lowest temperatures. In the previous ESR down to 0.5 K, this mode was clearly found for H // c. in which the magnitude of the gap is largest. In the present work. the achievement of low temperatures enabled us to observe a smaller gap in H // b by suppressing the thermal excitation. The magnitude of the field-induced gap evaluated from the nonlinear field dependence of the mode shows good agreement with that determined by previous specific heat measurements.

DOI： 10.1143/JPSJ.70.2259

Web of Science

Scopus

H. Kato, M. Ishizone, T. Miyazaki, K. Koyama, H. Nojiri, M. Motokawa, T. Ishizaki . High-frequency ferromagnetic resonance in Nd<inf>2</inf>Fe<inf>14</inf>B/α-Fe nanocomposite films . IEEE Transactions on Magnetics37 ( 4 ) 2567 - 2569 2001年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

Thin-film magnets, composed of nanophase dispersed Nd2Fe14B and α-Fe have been synthesized by rf magnetron sputtering. With increasing α-Fe volume fraction VFe, the saturation magnetization increased linearly, while the coercivity decreased. Ferromagnetic resonance measurements were made by using a high-frequency and high-field ESR apparatus, which exhibited two absorption peaks. A model calculation of the resonance field was made for a simplified hard/soft two-sublattice system to analyze these results. Estimated values of the exchange-coupling constant are in good agreement with those deduced from micro-magnetic analysis of the magnetization curves.

DOI： 10.1109/20.951237

Web of Science

Scopus

Y. Oshima, H. Ohta, S. Okubo, K. Koyama, M. Motokawa, M. Tamura, Y. Nishio, K. Kajita . Fermi surface study of θ-(BEDT-TTF)<inf>2</inf>I<inf>3</inf> by cyclotron resonance measurements . Synthetic Metals120 ( 1-3 ) 853 - 854 2001年3月

記述言語：英語掲載種別：研究論文（学術雑誌）

Cyclotron resonances of quasi-two-dimensional organic conductor θ-(BEDT-TTF)2I3 have been observed by using Millimeter Vector Network Analyzer (MVNA), V- and W-Band Cavity at 0.5K. Two resonances are observed, and the mode coupling in the cavity suggests that the resonances are cyclotron resonances. Obtained effective masses 1.03me and 2.14me are assigned to be α and β orbits, respectively.

DOI： 10.1016/S0379-6779(00)00711-6

Web of Science

Scopus

K Koyama, H Fujii, T Goto, H Fukuda, Y Janssen . Magnetic phase transitions of Ce2Fe17 under high pressures and high magnetic fields . PHYSICA B294 168 - 171 2001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：ELSEVIER SCIENCE BV

Magnetization measurements have been performed on single-phase Ce2Fe17 with a rhombohedral structure under high pressures up to 1.2 GPa and in magnetic fields B up to 17T to clarify the pressure effect on the magnetic phase transitions. At 0.8 GPa, we observed at least seven magnetic phases in the B-T plane. The results obtained indicate that the hybridization between the Fe 3d- and Ce 4f-electron states plays an important role for the magnetic properties of Ce2Fe17. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(00)00634-7

Web of Science

Scopus

K. Koyama, H. Fujii, T. Goto, H. Fukuda and Y. Janssen, . Magnetic phase transitions of Ce2Fe17 under high pressure and high magnetic fields . Physica B294-295 168 - 171 2001年査読

T. Kanomata, T. Sasaki, T. Hoshi, T. Narita, T. Harada, H. Nishihara, T. Yoshida, R. Note, K. Koyama, H. Nojiri, T. Kaneko and M. Motokawa . Magnetic and electrical properties of Fe2+xV1-xAl . J. Alloys and Compounds317-318 390 - 394 2001年査読

K. Koyama, T. Sakon, H. Nojiri and M. Motokawa . Observation of new ESR mode at ultra low temperatures and CR of RE compounds by VNA . proceedings for 26th IRMMW (Toulouse 2001) 1 - 6 2001年査読

K. Koyama, T. Tomimatsu, M. Yoshida, D.X. Li and M. Motokawa . Cyclotron resonance of GdSb . J. Phys. Soc. Jpn.70 2371 - 2375 2001年査読

M. Yoshida, K. Koyama, T. Tomimatsu, M. Shirakawa, A. Ochiai and M. Motokawa . Cyclotron resonance of LaBi . J. Phys. Soc. Jpn.70 2078 - 2081 2001年査読

T. Sakon, H. Nojiri, K. Koyama, T. Asano, Y. Ajiro and M. Motokawa . Electron spin resonance study of Cu Benzoate using 3He-4He dilution refrigerator . J. Phys. Soc. Jpn.70 2259 - 2262 2001年査読

K. Koyama, M. Yoshida, D.X. Li and M. Motokawa . Magnetic resonance of GdP . J. Phys. Soc. Jpn.70 2774 - 2777 2001年査読

K. Koyama, M. Yoshida, T. Sakon, H. Nojiri, D.X. Li, T. Suzuki and M. Motokawa . ESR and CR measurements of Gd monopnictides . Physica B294-265 156 - 159 2001年査読

M. Yoshida, K. Koyama, H. Hiraga, Y. Endoh and M. Motokawa . High field ESR measurements of CoS2 . Physica B294-295 145 - 148 2001年査読

Y. Oshima, H. Ohta, S. Okubo, K. Koyama, M. Motokawa, M. Tamura, Y. Nishio and K. Kajita . High-field magnetooptical measurements of BEDT-TTF salts . Physica B294-295 431 - 434 2001年査読

Y. Oshima, H. Ohta, S. Okubo, K. Koyama, M. Motokawa, M. Tamura, Y. Nishio and K. Kajita, . Fermi surface study of θ-(BEDT-TTF)2I3 by cyclotron resonance measurements . Synth. Metals. 120 853 - 854 2001年査読

H. Ohta, Y. Oshima, T. Sakurai, S. Okubo, T. Tanaka, K. Koyama, M. Motokawa, H. Kikuchi, H. Nagasawa, J.P. Boucher . Observation of direct transition in S=1/2 quantum spin system Cu2(C5N12N2)2Cl4 by high field ESR . J. Magn. Magn. Mater. 226-230 439 - 440 2001年査読

H. Kato, M. Ishizone, T. Miyazaki, K. Koyama, H. Nojiri and M. Motokawa . High-frequency ferromagnetic resonance in Nd2Fe14B/α-Fe nanocomposite films . IEEE Trans. Magn.37 2567 - 2569 2001年査読

加藤宏明、石曽根昌彦、宮崎照宣、小山佳一、野尻浩之、本河光博 . 強磁性共鳴によるナノコンポジット磁石の交換結合の評価 . 日本応用磁気学会誌25 675 - 678 2001年査読

Keiichi Koyama, Hironobu Fujii . Nitrogen gas-solid reaction process and basic magnetism of the interstitially modified rare-earth transition-metal nitrides and . Physical Review B - Condensed Matter and Materials Physics61 9475 - 9493 2000年1月

In this paper, we present our recent results of studies of the nitrogen absorption process, magnetization measurements, and neutron powder-diffraction measurements for interstitially modified nitrides (Formula presented) Ce, Nd, and Sm) and (Formula presented) (1) The studies of nitrogen absorption rates in the (Formula presented) under various (Formula presented)-gas pressure up to 6 MPa indicated that the nitrogen absorption into grain interior is promoted by diffusion of nitrogen atoms under low (Formula presented)-gas pressure, while under high (Formula presented)-gas pressure, the nitrogen absorption is promoted by the grain growth of fully nitrogenated phase (Formula presented) rather than the diffusion, making high-pressure nitrogenation effective for synthesizing high-quality nitrides. (2) The high-field magnetization measurements of the (Formula presented) and (Formula presented) single crystals at 4.2 K indicated that interstitial modification of nitrogen atoms gives rise to a strong enhancement of crystalline electric field (CEF) acting on R atoms, leading to almost three times larger CEF-parameter (Formula presented) upon nitrogenation. (3) Neutron powder-diffraction studies of (Formula presented) and (Formula presented) with rhombohedral structure indicated that the N atoms fully occupy at the (Formula presented) site. The introduction of N atoms into (Formula presented) brought such a strong modification in the Fe magnetic moment that the moment of the (Formula presented) atoms being the nearest to the (Formula presented) atoms is the smallest, whereas the (Formula presented) and/or (Formula presented) atoms being relatively farther from the (Formula presented) atoms have the largest moments at 10 K. The results obtained are discussed on the basis of the calculated electronic band structures. © 2000 The American Physical Society.

DOI： 10.1103/PhysRevB.61.9475

Scopus

K. Koyama, T. Goto, T. Kanomata and R. Note . Observation of an itinerant metamagnetic transition in MnSi under high pressure . Phys. Rev. B62 986 - 991 2000年査読

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