研究者詳細 - 武田　直也

論文 - 武田　直也

分割表示 130 件中 61 - 80 件目／全件表示 >>

Ru-NQR studies on filled skutterudite compounds RRu4P12 (R = La, Nd, Sm) 査読

S. Masakia, T. Mito, M. Takemura, S. Wada, H. Harima, D. Kikuchi, H. Sato, H. Sugawara, N. Takeda, G. -q. Zheng

PHYSICA B-CONDENSED MATTER 403 ( 5-9 ) 1630 - 1632 2008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 BV

We report nuclear quadrupole resonance (NQR) studies on Ru-sites of filled skutterudite compounds RRuR12 (R = La, Nd, Sm) in zero magnetic field. For NdRu4P12, the Ru-101-NQR signal disappears below T-C = 1.6 K, which is indicative of the transformation into the ferromagnetically ordered ground state. For SmRu4P12, a single Ru-101-NQR line splits into two lines below the metal-insulator transition temperature T-MI = 16.5 K with the intensity ratio of 3 : 1. This result gives evidence that there are two inequivalent Ru-sites with different electric field gradient. The intensity ratio leads to a conclusion that the symmetry is lowered below T-MI from a cubic Im (3) over bar space group to a trigonal M one. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.10.205

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31P-NMR study in single crystal SmRu4P12 査読

S.Masaki 他

J.Phys.Soc.Jpn.;SuppleA. 77 206 - 208 2008年1月

Rattling in Clathrate Compounds of ROs4Sb12 and R3Pd20Ge6 査読

Y.Nemoto, T.Yanagisawa 他

J.Phys.Soc.Jpn.Supple.A 77 153 - 158 2008年1月

Elastic Quadrupole Effect in Clathrate Compound Pr3Pd20Si6 査読

T.Yanagisawa 他

J.Phys.Soc.Jpn.,SuppleA 77 263 - 265 2008年1月

Raman Scattering Study of Filled Skutterudite Compounds 査読

N.Ogita 他

J.Phys.Soc.Jpn.;Supple.A 77 251 - 253 2008年1月

Metamagnetism of ferromagnetic Kondo compound SmFe4P 12 査読

Naoya Takeda, Hiroyuki Mitamura, Koichi Kindo

Journal of the Physical Society of Japan 77 209 - 210 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：Physical Society of Japan

SmFe4P12 is a novel ferromagnetic heavy fermion compound with a Curie temperature Tc of 1.6K. The electronic specific heat coefficient is 370 mJ/mol·K2. The magnetic susceptibility of La1-xSmxFe4P12 (0.6 ≤ x ≤ 0.85) with a paramagnetic ground state shows a broad maximum around 15K. This phenomenon reminds us the case of CeRu2Si 2 which is in the boundary of itinerant and localized 4f-state. We measured the magnetization up to 42T and found metamagnetic crossover at 22T. The metamagnetism disappears with increasing temperature. Possible mechanism of the metamagnetism is discussed. ©2008 The Physical Society of Japan.

DOI： 10.1143/JPSJS.77SA.209

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Ultrasonic Study of Rattling and Tunneling in Clathrate Compounds R3Pd20X6 (R=La, Ce; X=Si, Ge). 査読

T.Watanabe, T.Yamaguchi, Y.Nemoto, T.Goto, N.Takeda, O.Suzuku, H.Kitazawa

Journal of Magnetism and Magnetic Materials 310 948 - 950 2007年12月

Antiferroquadrupolar ordering and anisotropic magnetic phase diagram of dysprosium palladium bronze, DyPd3S4 査読

Eiichi Matsuoka, Takashi Tayama, Toshiro Sakakibara, Zenji Hiroi, Naoki Shirakawa, Naoya Takeda, Masayasu Ishikawa

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 ( 8 ) 0084717(7) 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：PHYSICAL SOC JAPAN

From the measurements of magnetization and specific heat, we constructed B-T phase diagrams of single-crystalline DyPd3S4 which is known to exhibit antiferroquadrupolar (AFQ) and antiferromagnetic (AFM) ordering at low temperatures. The phase diagrams are found to be highly anisotropic and reentrant, which are typical of rare-earth compounds exhibiting multipolar ordering. The crystalline electric field (CEF) scheme of Dy3+ in DyPd3S4 was deduced from the specific heat and magnetization measurements of the Y-diluted compounds Dy1-xYxPd3S4 (0.1 <= x <= 0.9) and discussed in detail. The CEF ground state was determined to be the orbitally-degenerated quartet 17670), and the overall splitting width was estimated to be about 104 K. No correlation was found between the anisotropy of To and that of the Zeeman splitting width of the ground quartet Gamma((1))(67).

DOI： 10.1143/JPSJ.76.084717

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Investigation of SmFe4P12 at pressures to 8 GPa 査読

K.Kurita, M.Hedo, Y.Uwatoko, N.Takeda, S.W.Tozer

J.Phys.Soc.Jpn.,Supple.A 76 64 - 65 2007年6月

Observation of symmetry lowering associated with the metal-insulator transition in SmRu4P12 by Ru-101-NQR 査読

Satoru Masaki, Takeshi Mito, Masayuki Takemura, Shinji Wada, Hisatomo Harima, Daisuke Kikuchi, Hideyuki Sato, Hitoshi Sugawara, Naoya Takeda, Guo-qing Zheng

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 ( 4 ) 043714-1 - 043714-4 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：PHYSICAL SOC JAPAN

We report the results of NQR (nuclear quadrupole resonance) study on SmRu4P12, one of a few candidates for materials showing octupolar ordering. In this study, we firstly succeeded in observing the Ru-101-NQR signal in filled skutterudite compounds RRu4P12 (R: rare earth). A single Ru-101-NQR signal splits into two resonance lines, having intensity ratio of 3 : 1, just below the metal-insulator (M-I) transition temperature of 16.5 K. This result gives convincing evidence for symmetry lowering in the ordered state of this compound, namely the cubic Im(3) over bar space group for the filled skutterudite compounds is lowered to the trigonal R(3) over bar. The model of the ordered structure characterized by a wave vector q = (1, 0, 0) satisfactorily explains the observed phenomena in the present study and the M-I transition in this compound.

DOI： 10.1143/JPSJ.76.043714

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NMR study of the successive two phase transitions in SmRu4P12 査読

Masaki Satoru, Mito Takeshi, Shinji Wada, Naoya Takeda, Daisuke Kikuchi, Hideyuki Sato, Hitoshi Sugawara, Guo-qing Zheng

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 ( 2 ) E175 - E177 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

In order to investigate the microscopic origin of the transitions at T-MI similar to 16.5K and T* similar to 14K in filled skutterudite compound SmRu4P12, we have carried out P-31-NMR measurements using a single crystal sample. The drastic change in the NMR line-shape below TMI was observed, which is attributed to the occurrence of some long-range magnetic ordering. The order is probably associated with octupole ordering as indicated from the NMR measurements on the powder sample of SmRu4P12. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.128

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Raman scattering study of the skutterudite compounds 査読

N. Ogita, R. Kojima, Y. Takasu, T. Hasegawa, T. Kondo, M. Udagawa, N. Takeda, T. Ikeno, K. Ishikawa, H. Sugawara, D. Kikuchi, H. Sato, C. Sekine, I. Shirotani

Journal of Magnetism and Magnetic Materials 310 ( 2 ) 948 - 950 2007年3月

記述言語：英語掲載種別：研究論文（学術雑誌）

Raman scattering of skutterudite compounds RT4 X12 (R = La, Ce, Pr, Nd, Sm and Yb, T = Fe, Ru and Os, X = P and Sb) have been measured. All first-order Raman active phonons are observed and are assigned as the pnictogen vibrations. At the low energy region, the second-order phonons, including the vibration of the rare-earth ions with a flat phonon dispersion, are observed in the spectra of SmRu4 P12 and ROs4 Sb12. The second-order phonons can be observed for the sample with the larger cage space. The large displacement in the large cage space and the large density of state due to the flat phonon dispersion increase the intensity of the second-order Raman scattering process. The intensity of the second-order phonon are also affected by the valence of the rare-earth ions. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.159

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Crystalline electric field effect and magnetic properties of CeRhSi3 single crystal 査読

Y. Muro, M. Ishikawa, K. Hirota, Z. Hiroi, N. Takeda, N. Kimura, H. Aoki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 ( 3 ) 033706-1 - 033706-3 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：PHYSICAL SOC JAPAN

We have studied the crystalline electric-field effect of the noncentrosymmetric heavy-fermion antiferromagnet CeRhSi3 by measuring the magnetic susceptibility chi(T), specific heat C-p(T) and inelastic neutron scattering. The 4f level scheme determined from X agrees with a magnetic excitation observed in the inelastic neutron spectra and the Schottky anomaly in the magnetic part of C, Moreover, we have measured C, under various magnetic fields B up to 8 T and observed that the Neel temperature T-N decreases proportionally to B-2 for B || a-axis while the B dependence of T-N is rather small for B || c-axis. This anisotropic behavior suggests that the antiferromagnetically ordered moments lie in the tetragonal c-plane.

DOI： 10.1143/JPSJ.76.033706

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Observation of two spin gap energies in the filled skutterudite compound CeOs(4)Sb(12) 査読

D. T. Adroja, J. -G. Park, E. A. Goremychkin, K. A. McEwen, N. Takeda, B. D. Rainford, K. S. Knight, J. W. Taylor, Jeongmi Park, H. C. Walker, R. Osborn, Peter S. Riseborough

PHYSICAL REVIEW B 75 ( 1 ) 014418(1) - 014418(8) 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：AMER PHYSICAL SOC

The optical conductivity of the Kondo insulator compound CeOs(4)Sb(12) reveals the formation of a 70 meV charge gap below 160 K. It also exhibits a weak shoulderlike structure at 30 meV, below 60 K. We have investigated CeOs(4)Sb(12) by inelastic neutron scattering techniques using incident neutron energies (E(i)) of 23 and 200 meV, at 5 and 176 K. Our measurements with E(i) = 200 meV show magnetic scattering centered near 50-60 meV and low-Q (similar to 3.8 angstrom(-1)) at 5 K, in addition to the continuum of magnetic scattering observed at 176 K. This clearly indicates the opening of a spin gap (or pseudogap ) of the order of 50 meV at 5 K in the strongly renormalized band near the Fermi energy. Furthermore, measurements with E(i) = 23 meV did not reveal any evidence of magnetic excitations below 20 meV, consistent with the scenario of a spin gap in CeOs(4)Sb(12). However, the estimated magnetic scattering deduced from the E(i) = 200 meV data reveals the presence of broad magnetic scattering between 25 and 80 meV centered near 27 meV, indicating a second energy scale with a gap energy of 27 meV. We interpret the 50 meV energy scale in terms of a direct gap, while the 27 meV energy scale corresponds to an indirect gap across the two hybridized bands. This gap energy of 27 meV is in good agreement with the so-called universal energy scale versus single ion Kondo temperature plot. We present the general features of spin gap systems such as CeOs(4)Sb(12) and CeRu(4)Sb(12), and discuss the role of crystal field excitations regarding the spin gap formation based on a theoretical model.

DOI： 10.1103/PhysRevB.75.014418

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Magnetic Instability around the Quantum Critical Point in CeCoGe1-xSix(0<x<3) 査読

D.Eom, N. Takeda, M.Ishikawa

J.Phys.Soc.Jpn. vol.75,No.9 093706(1) - 093706(3) 2006年12月

Rattling and tunneling of off-center local oscillator in clathrate compounds 査読

Terutaka Goto, Yuichi Nemoto, Takashi Yamaguchi, Tatsuya Yanagisawa, Takafumi Ueno, Tomoyuki Watanabe, Naoya Takeda, Osamu Suzuki, Hideaki Kitazawa, Hitoshi Sugawara, Hideyuki Sato

PHYSICA B-CONDENSED MATTER 383 ( 1 ) 115 - 119 2006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：ELSEVIER SCIENCE BV

We have investigated an off-center local oscillator of a guest atom in cage of clathrate compounds R3Pd20Ge6 (R = La, Ce, Pr, Nd) and a filled skutterudite PrOs4Sb12 using ultrasonic measurements. The observation of ultrasonic dispersions in transverse C-44 mode of R3Pd20Ge6 and in transverse (C-11 - C-12)/2 mode of PrOs4Sb12 revealed the rattling of the off-center oscillator characterized by a relaxation time with Arrhenius-type temperature dependence. A low-temperature softening of C-44 in La3Pd20Ge6 below 3 K down to 20 mK and a softening of (C-11 - C-12)/2 in PrOs4Sb12 above the heavy Fermion superconducting transition indicate the charge fluctuation due to the degenerate off-center oscillators. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.03.071

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Raman scattering investigation of skutterudite compounds 査読

N. Ogita, T. Kondo, T. Hasegawa, Y. Takasu, M. Udagawa, N. Takeda, K. Ishikawa, H. Sugawara, D. Kikuchi, H. Sato, C. Sekine, I. Shirotani

PHYSICA B-CONDENSED MATTER 383 ( 1 ) 128 - 129 2006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：ELSEVIER SCIENCE BV

Raman scattering spectra of filled skutterudite RT4X12 (R = La, Ce, Pr, Nd, Sm and Y, T = Fe, Ru and Os, and X = Sb and P) and unfilled skutterudite CoP3 have been measured. All first-order Raman active phonons, which are due to the vibration of pnictogens, are observed. In addition, the crystal field excitations in PrRu4P12 spectra and the second-order phonons including rare-earth vibrations in SmRu4P12 and ROs4Sb12 are also observed. The second-order phonons can be observed for the sample with the larger cage space. The peak intensity of the second-order phonons decreases with decreasing temperature and vanishes at low temperature. Such a temperature dependence suggests that the second-order phonons are thermally excited and due to independent vibrations of the rare-earth ions, that is rattler motion. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.03.076

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Microscopic investigation of possible multipole ordering in SmRu4P12 by P-31-NMR 査読

Satoru Masaki, Takeshi Mito, Naomi Oki, Shinji Wada, Naoya Takeda

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 ( 5 ) 053708-1 - 053708-5 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：PHYSICAL SOC JAPAN

To elucidate microscopically the metal-insulator transition (T-MI similar to 16.5 K) and an additional transition (T* similar to 15 K) in Sm-based filled skutterudite compound SmRu4R12, we have carried out P-31-NMR (nuclear magnetic resonance) at various fields from 0.8 to 11 T. The peaks in the spin lattice relaxation rate 1/T-1 observed at T-MI and T* under similar to 7T indicate that there are different magnetic fluctuation modes in SmRu4P12: one freezes below T-MI and the other does below T*. The anomalous field and temperature dependences of the NMR spectrum are explained in terms of the occurrence of multipole ordering. We have examined the two possible scenarios to account for the experimental results, and both cases suggest that the M-I transition involves octapole ordering.

DOI： 10.1143/JPSJ.75.053708

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Ultrasonic dispersion and off-center rattling in heavy fermion superconductor PrOS4Sb12 査読

Yuichi Nemoto, Takafumi Ueno, Naoya Takeda, Takashi Yamaguchi, Tatsuya Yanagisawa, Terutaka Goto, Hitoshi Sugawara, Hideyuki Sato

PHYSICA B-CONDENSED MATTER 378-80 184 - 186 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

Ultrasonic attenuation measurements have been firstly performed for a large single crystal of PrOs4Sb12 with the dimensions of 5.97 x 0.6 x 0.6 mm(3). Remarkable frequency dependence around 20-40K has been observed in the elastic constant and attenuation coefficient of the longitudinal C-11 mode associated with E-g symmetry strain in part, which results from a thermally activated off-center rattling with E-g symmetry of a Pr ion inside a Sb icosahedron cage. Parameters of a characteristic time tau(0) = 3.1 x 10(-11) s and an activation energy E = 225 K were obtained. This E-g rattling involving a local charge fluctuation inside a Sb cage periodically arranged may couple to the conduction electrons. As a result, the electron-phonon coupling would lead to heavy fermion and its superconductivity in PrOs4Sb12. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.070

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NMR study of unique properties in SmRu4P12 査読

T Mito, S Masaki, N Oki, S Noguchi, S Wada, N Takeda, D Kikuchi, H Sato, H Sugawara, GQ Zheng

PHYSICA B-CONDENSED MATTER 378-80 224 - 225 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

We have carried out P-31-NMR (nuclear magnetic resonance) studies on Sm-based filled skutterudite compounds SmRu4P12. The measurements of NMR spectrum at various fields (H's) give evidence that spontaneous internal field occurs below the metal-insulator transition temperature T-M1 similar to 16.5 K. Concomitantly H-induced local field was observed between two successive transition temperatures, T* (similar to 14K) < T < T-M1, suggesting that some multipole ordering coexists with dipole ordering in this compound. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.083

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