Magnetic Ordering and Structural Phase Transitions of Nd3T4Sn13 (T = Rh and Ir)
Ami Shimoda; Kazuaki Iwasa; Keitaro Kuwahara; Hajime Sagayama; Hironori Nakao; Motoyuki Ishikado; Takashi Ohhara; Akiko Nakao; Akinori Hoshikawa; and Toru Ishigaki
JPS Conference Proceedings, 2023年05月23日, ［査読有り］
Gaps in topological magnon spectra: Intrinsic versus extrinsic effects
Seung-Hwan Do; Joseph A. M. Paddison; Gabriele Sala; Travis J. Williams; Koji Kaneko; Keitaro Kuwahara; Andrew F. May; Jiaqiang Yan; Michael A. McGuire; Matthew B. Stone; Mark D. Lumsden; and Andrew D. Christianson
PHYSICAL REVIEW B, 2022年08月24日, ［査読有り］
Magnetic Excitations in Chiral-Structure Phase of Ce3Ir4Sn13
Kazuaki Iwasa; Seiya Nakazato; Daisuke Hashimoto; Mami Shiozawa; Keitaro Kuwahara; Hajime Sagayama; Seiko Ohira-Kawamura; Naoki Murai; Devashibhai T. Adroja; and André M. Strydom
Journal of the Physical Society of Japan, 2021年11月02日, ［査読有り］
Helical and Collinear Spin-Density-Wave Orders in S = 1/2 One-dimensional Frustrated Chain Compound NaCuMoO4(OH) Investigated by Neutron Scattering
Shinichiro Asai; Takuma Oyama; Kazuhiro Nawa; Akiko Nakao; Koji Munakata; Keitaro Kuwahara; Masato Hagihala; Shinichi Itoh; Zenji Hiroi; Takatsugu Masuda
Physical Review B, 2020年04月28日, ［査読有り］
Single-Crystal Growth and Physical Properties of EuZn2Ge2
Masashi Kosaka; Shinji Michimura; Hikaru Hirabayashi; Ryosuke Numakura; Ryosuke Iizuka; Keitaro Kuwahara; Yoshiya Uwatoko
Journal of the Physical Society of Japan, 2020年04月08日, ［査読有り］
Successive Phase Transitions in R3Ir4Sn13 (R: La and Ce) Investigated Using Neutron and X-ray Diffraction
Seiya Nakazato; Kazuaki Iwasa; Daisuke Hashimoto; Mami Shiozawa; Keitaro Kuwahara; Hironori Nakao; Hajime Sagayama; Motoyuki Ishikado; Takashi Ohhara; Akiko Nakao; Koji Munakata; Ryoji Kiyanagi
JPS Conf. Proc., 2020年03月19日, ［査読有り］
URu2Si2 under intense magnetic fields: From hidden order to spin-density waveW. Knafo; D. Aoki; G.W. Scheerer; F. Duc; F. Bourdarot; K. Kuwahara; H. Nojiri; L.-P. Regnault; J.Flouquet, A review of recent state-of-the-art pulsed field experiments performed on URu2Si2 under a magnetic field applied along its easy magnetic axis c is given. Resistivity, magnetization, magnetic susceptibility, Shubnikov-de Haas, and neutron diffraction experiments are presented, permitting to emphasize the relationship between Fermi surface reconstructions, the destruction of the hidden-order and the appearance of a spin-density wave state in a high magnetic field., Elsevier B.V.
Physica B, 2018年05月01日,
［査読有り］ Structure of the magnetic excitations in the spin-1/2 triangular-lattice Heisenberg antiferromagnet Ba3CoSb2O9S. Ito; N. Kurita; H. Tanaka; S. Ohira-Kawamura; K. Nakajima; S. Itoh; K. Kuwahara; K. Kakurai, A spin-1/2 triangular-lattice Heisenberg antiferromagnet (TLHAF) is a prototypical frustrated quantum magnet, which exhibits remarkable quantum many-body effects that arise from the synergy between spin frustration and quantum fluctuation. The ground-state properties of a spin-1/2 TLHAF are theoretically well understood. However, the theoretical consensus regarding the magnetic excitations is limited. The experimental study of the magnetic excitations in spin-1/2 TLHAFs has also been limited. Here we show the structure of magnetic excitations in the spin-1/2 TLHAF Ba3CoSb2O9 investigated by inelastic neutron scattering. Significantly different from theoretical expectations, the excitation spectrum has a three-stage energy structure. The lowest-energy first stage is composed of dispersion branches of single-magnon excitations. The second and third stages are dispersive continua accompanied by a columnar continuum extending above 10 meV, which is six times larger than the exchange interaction J = 1.67 meV. Our results indicate the shortcomings of the current theoretical framework., NATURE PUBLISHING GROUP
Nature Communications, 2017年08月10日,
［査読有り］ First report on the Electronic, Magnetic and thermal Properties of Filled Skutterudite YbOs4Sb12H. Kunitoshi; T. D. Matsuda; R. Midorikawa; R. Higashinaka; K. Kuwahara; Y. Aoki; H. Sato, Single crystals of the filled skutterudite compound YbOs4Sb12, for which no information except the lattice constant exists, have been investigated by measurements of the electronic transport properties, magnetic susceptibility, and specific heat. It is confirmed that the ground state is a Fermi liquid state with the Sommerfeld coefficient. similar to 40 mJ= K-2 mol. Near 50 K, a sharp change in the slope appears in the temperature dependences of both the electrical resistivity and the Hall coefficient, and the magnetic susceptibility shows a shallow maximum. The Einstein temperature (similar to 40 K) determined by the specific heat measurement is less than the lowest value ever reported for SmOs4Sb12. The large deviation from the reported linear correlation between the Einstein temperature and the size of the effective free space for the guest ion vibration within the Os4Sb12 cage was examined by extending the comparison to the reported Ce-, Pr-, Eu-, and Yb- based filled skutterudites., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2016年,
［査読有り］ Field-induced spin-density wave beyond hidden order in URu2Si2W. Knafo; F. Duc; F. Bourdarot; K. Kuwahara; H. Nojiri; D. Aoki; J. Billette; P. Frings; X. Tonon; E. Lelièvre-Berna; J. Flouquet; and L.-P. Regnault, URu2Si2 is one of the most enigmatic strongly correlated electron systems and offers a fertile testing ground for new concepts in condensed matter science. In spite of 430 years of intense research, no consensus on the order parameter of its low-temperature hidden-order phase exists. A strong magnetic field transforms the hidden order into magnetically ordered phases, whose order parameter has also been defying experimental observation. Here, thanks to neutron diffraction under pulsed magnetic fields up to 40 T, we identify the field-induced phases of URu2Si2 as a spin-density-wave state. The transition to the spin-density wave represents a unique touchstone for understanding the hidden-order phase. An intimate relationship between this magnetic structure, the magnetic fluctuations and the Fermi surface is emphasized, calling for dedicated band-structure calculations., NATURE PUBLISHING GROUP
Nature Communications, 2016年,
［査読有り］ Intermultiplet transitions in filled skutterudite SmFe4P12S. Konno; A. Suzuki; K. Nihei; K. Kuwahara; D. Kawana; T. Yokoo and S. Itoh, The intermultiplet transitions in filled skutterudite SmFe4P12 are studied by magnetization and time-of-flight inelastic neutron scattering experiments. In neutron scattering experiments by using high energy neutrons for reducing huge neutron absorption of natural Sm, a small inelastic peak has been observed around similar to 80 meV at low temperature. The scattering vector dependence of intensity of this peak agrees with the theoretical inelastic structure factor for the intermultiplet transition from the ground J = 5/2 multiplet to the excited J = 7/2 multiplet in Sm3+ ion. Interestingly, the energy splitting is much smaller than the free Sm3+ ion value. This is also comparable with that estimated by the inverse magnetic susceptibility. This large reduction of the energy splitting might be due to the strong c-f mixing in SmFe4P12., IOP PUBLISHING LTD
Journal of Physics: Conference Series, 2015年
Science from the Initial Operation of HRC
S. Itoh; T. Yokoo; T. Masuda; H. Yoshizawa; M. Soda; Y. Ikeda; S. Ibuka; D. Kawana; T. J. Sato; Y. Nambu; K. Kuwahara; S. Yano; J. Akimitsu; Y. Kaneko; Y. Tokura; M. Fujita; M. Hase; K. Iwasa; H. Hiraka; T. Fukuda; K. Ikeuchi; K. Yoshida; T. Yamaguchi; K. Ono; Y. Endoh
JPS Conference Proceedings, 2015年
Electronic State of CeFe4As12 Investigated by Using Single Crystals Grown under High Pressure of 4 GPaY. Ogawa; H. Sato; M. Watanabe; T. Namiki; S. Tatsuoka; R. Higashinaka; Y. Aoki; K. Kuwahara; J. Yamaura; and Z. Hiroi, The electronic transport, magnetic, and specific heat measurements on CeFe4As12 single crystals grown under high pressure of similar to 4 GPa have been performed, in order to clarify the reported contradictory results on the electronic state between the single crystals grown under minute pressure of similar to 4 MPa and polycrystalline samples synthesized under high pressure (similar to 4 GPa). Special emphasis was put on the huge sample dependent physical properties reported in the former, which was attributed to huge sample dependent lattice constant and morphology of grown single crystals. We found similar sample-dependent electronic transport properties also in our high pressure grown single crystals with little sample dependence of the lattice constant, suggesting that neither the lattice constant nor morphology has direct connection with the electronic properties in CeFe4As12. Based on these facts, the reason for such a sensitive sample-dependent electronic transport properties of CeFe4As12 is discussed, in correlation with the marginal Kondosemiconducting ground state of this material., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2014年02月21日
Magnetic Structure of Phase II in U(Ru0.96Rh0.04)(2)Si-2 Determined by Neutron Diffraction under Pulsed High Magnetic FieldsK. Kuwahara; S. Yoshii; H. Nojiri; D. Aoki; W. Knafo; F. Duc; X. Fabreges; G. W. Scheerer; P. Frings; G. L. J. A. Rikken; F. Bourdarot; L. P. Regnault; J. Flouquet, We report neutron diffraction measurements on U(Ru0.96Rh0.04)(2)Si-2 single crystal under pulsed high magnetic fields up to 30 T applied along the tetragonal c axis. The high-field experiments revealed that the field-induced phase II above 26 T corresponds to a commensurate up-up-down ferrimagnetic structure characterized by the wave vector q = (2/3, 0, 0) with the magnetic moments parallel to the c axis, which naturally explains the one-third magnetization plateau and the substantially changed Fermi surface in phase II. This a-axis modulated magnetic structure indicates that the phase II near the hidden order phase is closely related to the characteristic incommensurate magnetic fluctuations at Q(1) = (0.6, 0, 0) in the pure system URu2Si2, in contrast to the pressure-induced antiferromagnetic order at Q(0) = (1, 0, 0)., AMER PHYSICAL SOC
PHYSICAL REVIEW LETTERS, 2013年05月
Magnetic Excitation in Totally Symmetric Staggered Ordered Phase of PrFe4P12K. Iwasa; L. Hao; M. Kohgi; K. Kuwahara; J.-M. Mignot; H. Sugawara; Y. Aoki; T.D. Matsuda; and H. Sato, We report inelastic neutron scattering results for single-crystalline samples of PrFe4P12, which undergoes a transition from the heavy-electron phase to the antiferro-type nonmagnetic ordered phase. In contrast to the quasielastic magnetic response observed in the heavy electron phase, the well-defined inelastic peaks located at 1.5 and 3 meV are superimposed in the ordered phase. The maximum spectral intensity appears at the Brillouin zone center for the original Im (3) over bar structure, and the minimum spectral intensity appears at the zone boundaries including the ordering vector q(0) = (1, 0, 0). The evolution of the 1.5 meV peak with an applied magnetic field in the ordered phase is in agreement with excitations between 4f-electron crystalline-field-splitting levels, while the 3 meV peak is smeared out rapidly. The spectra are consistent with the recently proposed staggered ordering of a Pr site with well-localized f-electrons and that with a Kondo-singlet-like state, which are represented as the totally symmetric state accompanied by the charge modulation of carriers., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2012年
Neutron scattering study on magnetic ordering in a partially rare-earth filled skutterudite PrxFe4Sb12K. Iwasa; T. Orihara; K. Saito; K. Tomiyasu; Y. Murakami; H. Sugawara; K. Kuwahara; H. Kimura; R. Kiyanagi; Y. Ishikawa; Y. Noda; Y. Aoki; H. Sato and M. Kohgi, Neutron scattering studies reveal that a crystal-field-splitting ground state of Pr3+ 4f(2) electrons in a partially filled PrxFe4Sb12 (x < 1) is a triplet. A magnetically ordered structure below 4 K consists of both magnetic moments at the Pr and Fe sites, in contrast to the x = 1 system without any magnetic ordering due to the 4f-electron singlet ground state., IOP PUBLISHING LTD
Journal of Physics: Conference Series, 2012年
Renormalized Motion of Dysprosium Atoms Filling Boron Cages of DyB6K. Iwasa; K. Kuwahara; Y. Utsumi; K. Saito; H. Kobayashi; T. Sato; M. Amano; T. Hasegawa; N. Ogita; M. Udagawa; S. Tsutsui; and A.Q.R. Baron, The lattice dynamics of DyB6 are investigated by an inelastic X-ray scattering technique. The measured phonon modes are dominated by the motion of Dy ions in oversized boron cages. These soften remarkably as temperature is decreased, with the energy of the longitudinal phonon for the propagation vector q(1) = (1/2, 0, 0) decreasing by 29% from 300 K down to the phase transition temperature of 31 K. The dispersion relation curves show kinklike anomalies at q(k) = (0.38, 0.38, 0). The observed phenomena are very similar to those previously observed in GdB6 [Iwasa et al.: Phys. Rev. B 84 (2011) 214308]. We note analogous phonon anomalies in the heavier rare-earth hexaboride systems, owing to the interplay between the motion of rare-earth atoms and the electronic state, particularly characterized by the Friedel oscillation., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2012年
Strong Effect of Yb Filling Fraction on the Magnetic Ground Sate of the Filled Skutterudite YbFe4Sb12T. Saito; H. Sato; K. Tanaka; S. Tatsuoka; M. Ueda; R. Higashinaka; T. Namiki; Y. Aoki; Y. Utsumi; K. Kuwahara; and T. Hosoya, YbFe4Sb12 single crystals with the Yb-site filling fraction close to 100% have been successfully synthesized by the Sb self-flux method under a pressure of 4 GPa. The grown single crystals do not exhibit ferromagnetic ordering down to the lowest temperature investigated, in contrast with the ferromagnetic transition reported for Yb-deficient single crystals grown at ambient pressure. The electronic specific heat coefficient of the present crystals is evidently smaller than those reported for Yb-deficient samples, indicating that the Fermi energy is located at the high-energy side of a peak in the electronic density of states dominated by the contribution of Fe-3d electrons. Therefore, the appearance of the ferromagnetic state in the Yb-deficient samples can be naively understood within the simple Stoner-type argument. Marked enhancement of the positive magnetoresistance was found in the temperature region where the spin-fluctuation scattering of conduction electrons dominates., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2011年
Motion of the guest ion as precursor to the first-order phase transition in the cage system GdB6K. Iwasa; R. Igarashi; K. Saito; C. Laulhé; T. Orihara; S. Kunii; K. Kuwahara; H. Nakao; Y. Murakami; F. Iga; M. Sera; S. Tsutsui; H. Uchiyama; and A.Q.R. Baron, The motion of guest Gd ions in oversized boron cages in GdB6 was investigated from phonon spectra measurements obtained by inelastic x-ray scattering. The measured phonon modes soften by about 10% from 300 K down to T-N = 16 K, in particular, the longitudinal phonon for the propagation vector q(1) = (1/2,0,0) that characterizes the distorted structure below T-N. Besides, the dispersion relation curves show kinklike anomalies at q(k) = (0.38,0.38,0). The observed results imply that the motion of the guest Gd ion interplays with the f electrons magnetoelastically and with carriers via Fermi surface nesting. The anomalous properties previously reported for this material far above T-N originate from the strong electron-phonon coupling, which causes the motion of guest ions as precursors to the first-order phase transition., AMER PHYSICAL SOC
Physical Review B, 2011年
Pressure-Induced Antiferromagnetic Order in Filled Skutterudite PrFe4P12 Studied by Single-Crystal High-Pressure Neutron DiffractionT. Osakabe; K. Kuwahara; D. Kawana; K. Iwasa; D. Kikuchi; Y. Aoki; M. Kohgi and H. Sato, The order parameter in the pressure-induced insulating phase of the filled skutterudite compound PrFe4P12 has been investigated using a high-pressure single-crystal neutron diffraction technique. Clear evidence of the antiferromagnetic order with the propagation vector q = (1, 0, 0) was observed in the insulating phase above 2.7 GPa. The q = (1, 0, 0) structure is identical with that in the nonmagnetic ordered phase below 2.5 GPa and with the nesting property of the Fermi surface. The observed magnetic moment of the Pr ion is 2 mu(B) and almost pressure-independent up to at least 4.2 GPa. The 2 mu(B) magnetic moment originates from the dipole in the low-lying quasi-quartet crystal field state. The pressure-induced antiferromagnetic structure at 3.2 GPa is suppressed by applying a magnetic field of about 1.5 T, which is interpreted as a flop of magnetic moments into the alignment of the ferromagnetic state. This brings about a steep decrease in the electrical resistivity due to the disappearance of the antiferromagnetic superstructure., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2010年
Response of Itinerant-Electron Weak Ferromagnet LaFe4As12 to Pressure and Magnetic FieldS. Tatsuoka; M. Watanabe; B. Suemitsu; Y. Ogawa; A. Yamada; K. Matsubayashi; Y. Uwatoko; R. Higashinaka; Y. Aoki; T. Namiki; K. Kuwahara; and H. Sato, To investigate the quantum criticality and spin fluctuations in LaFe4As12, we have investigated the pressure and magnetic field dependences of electrical resistivity (rho). The Curie temperature T-C (similar to 5.2K at ambient pressure) is gradually suppressed by pressure (P) and disappears at approximately 2 GPa (similar to P-c). The coefficient A of the T-2 dependence of rho increases near P-c, and the exponent n of rho(T) similar to rho(0) + beta T-n changes into 5/3, which is expected for 3d ferromagnetic spin fluctuations. The low-field longitudinal magnetoresistance Delta rho/rho(T) is negative at low temperatures, as was commonly observed in typical itinerant-electron weak ferromagnets, reflecting a field-suppressed spin-fluctuation scattering. Above T-C, it becomes positive and shows a peak against magnetic field, which is hardly ascribable only to the ordinary positive magnetoresistance due to the Lorentz force on conduction electrons. Possible origins of the unexpected positive magnetoresistance are discussed by considering Kohler's plot for both the longitudinal and transverse magnetoresistances., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2010年
Current understanding of the heavy fermion superconductivity in PrOs4Sb12H. Sato; K. Tanaka; D. Kikuchi; T. Namiki; R. Higashinaka; Y. Aoki; M. Kohgi; H. Sugawara; K. Kuwahara; and K. Iwasa, PrOs4Sb12 is the first Pr-based heavy fermion superconductor exhibiting intriguing behavior both in the superconducting and normal states. To clarify the origin of the behavior, intensive studies have been made by variety of experimental techniques. As a result of intensive studies, the normal state properties have been mostly clarified, however, there still remain important questions on the superconducting state of this material. We discuss the present status of the understanding of superconducting state in relation with the normal state properties of this material. (C) 2009 Published by Elsevier B.V., ELSEVIER SCIENCE BV
Physica C, 2010年
Excitation spectrum of PrOs4Sb12 under a magnetic fieldS. Raymond; K. Kuwahara; K. Kaneko; K. Iwasa; M. Kohgi; A. Hiess; J. Flouquet; N. Metoki; H. Sugawara; Y. Aoki and H. Sato, The evolution of the magnetic excitation spectrum of the heavy fermion superconductor PrOs4Sb12 was studied by inelastic neutron scattering on crossing the critical field H-c2 for superconductivity at low temperature. The peak positions in energy and the peak intensities of the modes of the triplet split by magnetic field confirm the known crystal field parameters for PrOs4Sb12 in T-h symmetry. A selective broadening of the lineshape occurs on increasing the magnetic field: the linewidth of the upper mode of the triplet increases while the one of the middle mode does not., IOP PUBLISHING LTD
Journal of Physics: Condensed Matter, 2009年,
［査読有り］ Crystal Field Effect on Superconducting Transition in PrxOs4Sb12K.Tanaka; T. Namiki; A.Imamura; M. Ueda; T. Saito; S. Tatsuoka; R. Miyazaki; K. Kuwahara; Y. Aoki; and H. Sato, We have succeeded in growing PrxOs4Sb12 single crystals under high pressure (similar to 4GPa) for the first time, where the Pr site filling fraction is supposed to be enhanced. From the systematic Measurement of the transport, magnetic, and thermal properties on the grown single crystals, we found a marked decrease in the onset superconducting transition temperature T-c and a considerable increase in the 4f-electron crystal field (CF) energy splitting between the ground state and the first excited state (Delta(CF)), compared with those reported on the ambient-pressure grown single crystals. Furthermore, the mass enhancement is reduced in the high-pressure grown samples. The correlation between Delta(CF) and both T-c and mass enhancement indicates the crucial role of conduction electron scattering accompanied by the CF excitation in the superconductivity of this compound., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2009年
Magnetic octupole order in Ce0.7La0.3B6: A polarized neutron diffraction studyK. Kuwahara; K. Iwasa; M. Kohgi; N. Aso; M. Sera; F. Iga; M. Matsuura; and K. Hirota, Recently, in phase IV of CexLa1-xB6, weak but distinct superlattice reflections from the order parameter of phase IV have been detected by our unpolarized neutron scattering experiment [K. Kuwahara, K. Iwasa, M. Kohgi, N. Aso, M. Sera, F. Iga, J. Phys. Soc. Japan 76 (2007) 093702]. The scattering vector dependence of the intensity of superlattice reflections is quite unusual; the intensity is stronger for high scattering vectors. This result strongly indicates that the order parameter of phase IV is the magnetic octupole. However, the possibility that the observed superlattice reflections are due to lattice distortions could not be completely ruled out only on the basis of the unpolarized neutron scattering experiment. To confirm that the superlattice reflections are magnetic, therefore, we have performed a single crystal polarized neutron diffraction experiment on Ce0.7La0.7B6. The obtained result has clearly shown that the time reversal symmetry is broken by the order parameter of phase IV. This is further evidence for the magnetic octupole order in CexLa1-xB6. (C) 2009 Published by Elsevier B.V., ELSEVIER SCIENCE BV
Physica B, 2009年
Crystal field excitations in PrFe4Sb12 synthesized under high pressureK. Kuwahara; K. Tanaka; T. Saito; S. Tatsuoka; K. Iwasa; M. Watanabe; Y. Aoki; H. Sato; M. Kohgi; K. Iwasa; H. Sugawara; C. Stock and D. T. Adroja, In the filled skutterudite PrFe4Sb12 with high Pr-site filling fraction synthesized under high pressure, the bulk properties indicate a singlet ground state of the crystal field (CF) and no phase transition at low temperature, in contrast to the reported magnetic ordering in the samples with relatively low filling fraction. In order to clarify the CF states in PrFe4Sb12 microscopically, we have performed the inelastic neutron scattering experiment on the PrFe4Sb12 synthesized under high pressure. The CF level scheme obtained from the results is Gamma(1) (0 meV) - Gamma((2))(4) (2.3 meV) - Gamma((1))(4) (11.4 meV) - Gamma(23) (18 meV). Furthermore, it is found that the singlet-triplet states in low energy region have large off-diagonal matrix elements of quadrupoles, indicating the similarity of the CF states in the heavy fermion superconductor PrOs4Sb12., IOP PUBLISHING LTD
Journal of Physics: Conference Series, 2009年
Anomalous Electronic Behaviors in Ferromagnetic Kondo Lattice SmFe4P12D. Kikuchi; H. Sugawara; K. Tanaka; H. Aoki; M. Kobayashi; S. Sanada; K. Kuwahara; Y. Aoki; H. Shishido; R. Settai; Y. Ōnuki; H. Harima; and H. Sato, The electronic properties in SmFe4P12 have been investigated by means of the de Haas-van Alphen effect, transverse magnetoresistance, Hall effect, and band structure calculation. We have found a markedly large anisotropy in the cyclotron effective mass of the 47th band Fermi surface despite its nearly spherical shape. Moreover, this mass enhancement in SmFe4P12 is robust against magnetic field. The transverse magnetoresistance increases nearly quadratically with magnetic field for all field directions; this is unexpected for an ordinary uncompensated metal. The Hall coefficient is found to be 4-fold enhanced at low temperature compared with that at room temperature. These anomalies in transport properties are ascribed to the stronger enhancement of the cyclotron effective mass of the 48th band Fermi Surface., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2008年
Magnetic Excitations in Heavy Electron State of Filled Skutterudite PrxLa1-xFe4P12 (x = 1.00 and 0.85)K. Iwasa; L. Hao; T. Hasegawa; K. Horiuchi; Y. Murakami; J. Otsuki; Y. Kuramoto; M. Kohgi; K. Kuwahara; H. Sugawara; Y. Aoki; and H. Sato, PrFe4P12 exhibits clear heavy electron behaviors as well as the phase transition to an antiferro-type ordering of 4f electron state. In this paper, we report on inelastic neutron scattering results for powdered samples of PrxLa1-xFe4P12 (x = 1.00 and 0.85). A clear quasielastic magnetic response is observed, and no distinct signal is seen for crystal-field (CF) excitations in the heavy electron state. A model with strong hybridization between conduction electrons and Pr3+ 4f(2) electrons [J. Otsuki et al.: J. Phys. Soc. Jpn. 74 (2005) 200 and 2082] is consistent with the observed magnetic response. This result shows that the heavy electron behavior of PrxLa1-xFe4P12 (x = 1.00 and 0.85) originates from the Kondo effect associated with low-lying singlet-triplet CF states., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2008年
Itinerant-Electron Weak Ferromagnetism in La-Based Filled Skutterudite LaFe4As12S. Tatsuoka; H. Sato; K. Tanaka; M. Ueda; D. Kikuchi; H. Aoki; T. Ikeno; K. Kuwahara; Y. Aoki; H. Sugawara; and H. Harima, High-quality samples of LaFe4As12 with a residual resistivity ratio of 64 have been successfully synthesized under high pressure similar to 4GPa at 1100 K. The magnetization, specific heat, electrical resistivity, and Hall coefficient of the samples were measured. All the investigated properties exhibit evident anomalies at 5.2 K, thereby indicating a ferromagnetic transition. The large Rhodes-Wohlfarth ratio ( the ratio of the effective moment deduced from the Curie constant to the saturation moment per magnetic ion) of 32 suggests that LaFe4As12 is the first La-based filled skutterudite that exhibits itinerant-electron weak ferromagnetism, which is realized by the high density of states at the Fermi level D(E-F). The ferromagnetism is unexpected within the simple Stoner-type argument, because D(E-F) lies between those of an ordinary Pauli paramagnet LaFe4P12 and an enhanced Pauli paramagnet LaFe4Sb12 in the LaFe4X12 (X = P, As, Sb) series. We discuss this unexpected ferromagnetic transition on the basis of the difference in the spin-fluctuation strength between As- and Sb-based systems., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2008年
Crystal Field Excitations in the Filled Skutterudite NdOs4Sb12K. Kuwahara; M. Takagi; K. Iwasa; S. Itobe; D. Kikuchi; Y. Aoki; M. Kohgi; H. Sato and H. Sugawara, We have performed inelastic neutron scattering experiment on a powder sample of the ferromagnetic filled skutterudite compound NdOs4Sb12 in order to clarify the crystal-field (CF) states of 4f electrons in this system. At lowest temperature 15 K, two inelastic peaks have been observed at energy transfers 23.0 and 30.2meV. The intensity of these two peaks decreases with increasing temperature, as expected for excitations from the CF ground state. This observation of CF excitations evidences the localized character of 4f electrons in NdOs4Sb12. From this result and the bulk magnetic susceptibility of NdOs4Sb12, possible CF level schemes are discussed. (c) 2007 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2008年
Neutron scattering study on the field-induced O-xy-type antiferroquadrupolar ordering of the heavy-fermion superconductor PrOs4Sb12K. Kaneko; N. Metoki; R. Shiina; T. D. Matsuda; M. Kohgi; K. Kuwahara; N. Bernhoeft, Neutron scattering experiments have revealed a field-induced antiferroquadrupolar order parameter in the Pr-based heavy-fermion superconductor PrOs4Sb12. We observed the field-induced antiferromagnetic dipole moment with the propagation vector q=(100) for the applied field direction both H parallel to[110] and [001]. For H parallel to[110] at 8 T, it should be noted that the induced antiferromagnetic moment of 0.16(10) mu(B)/Pr orients parallel to the field within our experimental accuracy. This observation is strong evidence that the O-xy electric quadrupole is the primary order parameter for H parallel to[110]. A mean-field calculation, based on Gamma(1) singlet and Gamma((2))(4) excited triplet with the O-xy quadrupolar interaction, reproduces the induced moment direction and its field response. These facts indicate the predominance of O-xy-type antiferroquadrupolar interaction in PrOs4Sb12., AMERICAN PHYSICAL SOC
PHYSICAL REVIEW B, 2007年03月
Detection of Neutron Scattering from Phase IV of Ce0.7La0.3B6: A Confirmation of the Octupole OrderK. Kuwahara; K. Iwasa; M. Kohgi; N. Aso; M.i Sera and F. Iga, We have performed a single crystal neutron scattering experiment on Ce0.7La0.3B6 to microscopically investigate the order parameter of phase IV. Below the phase transition temperature 1.5 K of phase IV, weak but distinct superlattice reflections at the scattering vector K = (h/2, h/2, l/2) (h, l = odd number) have been observed for the first time by neutron scattering. The intensity of the superlattice reflections is stronger for high scattering vectors, which is quite different from the usual magnetic form factor of magnetic dipoles. This result directly evidences that the order parameter of phase IV has a complex magnetization density, consistent with the recent experimental and theoretical prediction in which the order parameter is the magnetic octupoles T-beta with Gamma(5) symmetry of the point group Oh. Neutron scattering experiments using short wavelength neutrons, as done in this study, could become a general method to study the high-rank multipoles in f electron systems., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2007年,
［査読有り］ Nonmagnetic Ground State in Fully Filled PrxFe4Sb12 (x=1.0) Synthesized under High PressureK. Tanaka; Y. Kawahito; Y. Yonezawa; D. Kikuchi; H. Aoki; K. Kuwahara; M. Ichihara; H. Sugawara; Y. Aoki; and H. Sato, We have succeeded in synthesizing the filled skutterudite PrxFe4Sb12 with the Pr-site filling fraction x close to 1 under high pressure. The residual resistivity of similar to 24 mu Omega.cm is several times smaller than that of samples with x similar to 0.8 synthesized under ambient pressure by independent research groups, indicating that highly improved sample quality can be achieved by reducing the Pr-site vacancy. From the transport, magnetic, and thermal measurements of the present sample with x similar to 1, we have found a singlet ground state of the crystalline electric field (CEF) for 4f-electrons and no phase transition down to 0.15 K, in contrast to the reported magnetic ordering near 5 K in the samples with x similar to 0.8. The effect of the Pr-site vacancy on the CEF level scheme and the 3d-electron density of states near the Fermi level is discussed as a possible origin of such a drastic change in the magnetic ground state., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2007年
Inelastic neutron scattering measurements in a quadrupolar ordering compound YbSbA. Oyamada; K. Kuwahara; K. Ohoyama; K. Iwasa; M. Kohgi and S. Maegawa, Inelastic neutron scattering measurements were performed to study the excitation spectra of a quadrupolar ordering compound YbSb. We observed the three peaks (12.5, 17 and 21 meV) around Gamma(6)-Gamma(8) excitations far above the quadrupolar ordering temperature (T-Q). This result suggests that the magnetic excitations have a dispersion rather than the splitting of Gamma(8) states at high temperatures. We also observed the strong q dependence in q scans at energy = 1 meV above T-Q. The observed q dependence above T-Q suggests that the theoretical approach beyond the molecular. field approximation is required in order to understand the magnetic properties of Yb monopnictides. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Journal of Magnetism and Magnetic Materials, 2007年
Elastic anomalies of UGe2K. Kuwahara; T. Sakai; M. Kohgi; Y. Haga and Y. Onuki, We have performed the ultrasonic sound velocity measurement on the single crystal of UGe2 in the temperature range 4.2-212 K at ambient pressure, focusing attention on the elastic behavior around the characteristic temperature T* approximate to 30 K. In the elastic constants for three modes c(11), c(55) and c(66), all modes show the hardening with a kink at the Curie temperature as decreasing temperatures. We found the elastic anomaly related to T* in the longitudinal c(11) mode. However, the anomaly around T* is very broad. Therefore, this result may suggest that T* is not related to a phase boundary of some second-order phase transition. On the other hand, no clear anomaly was observed around T* in the transverse c(55) and c(66) modes. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Journal of Magnetism and Magnetic Materials, 2007年
Structural Transformation on the Pressure-Induced Metal Insulator Transition in PrFe4P12D. Kawana; K. Kuwahara; M. Sato; M. Takagi; Y. Aoki; M. Kohgi; H. Sato; H. Sagayama; T. Osakabe; K. Iwasa and H. Sugawara, We report the first X-ray diffraction experiments of PrFe4P12 under high pressure. We discovered a symmetry lowering from cubic to orthorhombic or lower at the metal-insulator transition temperature, accompanied by a jump in the lattice constant, which indicates a first-order phase transition. The superlattice reflections at q = (1, 0, 0) observed in the low-pressure nonmagnetic ordered phase are found to disappear in the insulating phase. The temperature dependence of the lattice constant and the absence of the superlattice reflections are well explained by taking into account an antiferromagnetic ordering., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2006年,
［査読有り］ Unusual Electronic State of the Low-Carrier System CeSb under High Pressure Studied by Simultaneous Measurement of Electrical Resistivity and Lattice Parameter
A. Hannan; Y. Okayama; T. Osakabe; K. Kuwahara; M. Kohgi
Journal of the Physical Society of Japan, 2006年
The Unconventional Superconductivity of Skutterudite PrOs4Sb12: Time-Reversal Symmetry Breaking and Adjacent Field-Induced Quadrupole Ordering
Y. Aoki; T. Tayama; T. Sakakibara; K. Kuwahara; K. Iwasa; M. Kohgi; W. Higemoto; D.E. MacLaughlin; H. Sugawara; H. Sato
Journal of the Physical Society of Japan, 2006年
Magnetic and Transport Properties of Gd3Ir4Sn13 with Unique Crystal StructureC. Nagoshi; R. Yamamoto; K. Kuwahara; H. Sagayama; D. Kawana; M. Kohgi; H. Sugawara; Y. Aoki; H. Sato; T. Yokoo and M. Arai, We have performed an epithermal neutron scattering experiment along with magnetic susceptibility, resistivity, Hall effect, X-ray diffraction measurements on single crystals grown for the first time. The primary crystal structure was classified into the same structure as that of Yb3Rh4Sn13 with the space group Pm (3) over barn. However the crystal distortion characterized by (1/2, 1/2,0) was observed at room temperature by X-ray diffraction. The magnetic susceptibility and resistivity showed an anomaly at 10 K indicating a magnetic phase transition. The epithermal neutron diffraction clarified that an antiferromagnetic order with the propagation vector (100) exist below IOK. Overall features of transport properties in Gd3Ir4Sn13 are similar to those in La3Ir4Sn13., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2006年
Magnetic form factor of URu2Si2K. Kuwahara; M. Kohgi; K. Iwasa; M. Nishi; K. Nakajima; M. Yokoyama and H. Amitsuka, We report the field-induced magnetic form factor of the heavy-electron system URu2Si2 obtained by using polarized neutrons. The neutron experiments were performed on the two single crystals at 60 K by applying a magnetic field of 6 T along the tetragonal c-axis. The observed magnetic form factor is close to the theoretical 5f form factor of the free U3+ or U4+ ions calculated by the dipole approximation as other U-based intermetallic superconductors. However, the extrapolated value at sin theta/lambda = 0 (0.07 mu(B)/U) is smaller than the bulk magnetization value (0.10 mu(B)/N). Therefore, this result indicates some contribution other than 5f electrons to the bulk magnetization of URu2Si2. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2006年
Direct Observation of Quadrupolar Excitons in the Heavy-Fermion Superconductor PrOs4Sb12K. Kuwahara; K. Iwasa; M. Kohgi; K. Kaneko; N. Metoki; S. Raymond; M.-A. Measson; J. Flouquet; H. Sugawara; Y. Aoki and H. Sato, We report inelastic neutron scattering experiments performed to investigate the low energy magnetic excitations on single crystals of the heavy-fermion superconductor PrOs4Sb12. The observed excitation clearly softens at a wave vector Q=(1,0,0), which is the same as the modulation vector of the field-induced antiferro-quadrupolar ordering, and its intensity at Q=(1,0,0) is smaller than that around the zone center. This result directly evidences that this excitonic behavior is derived mainly from nonmagnetic quadrupolar interactions. Furthermore, the narrowing of the linewidths of the excitations below the superconducting transition temperature indicates the close connection between the superconductivity and the excitons., AMERICAN PHYSICAL SOC
Physical Review Letters, 2005年
Evolution of 4f-Electron States in the Metal-Insulator Transition of PrRu4P12K. Iwasa; L. Hao; K. Kuwahara; M. Kohgi; S.R. Saha; H. Sugawara; Y. Aoki; H. Sato; T. Tayama and T. Sakakibara, Magnetic excitations of the filled skutterudite PrRu4P12 exhibiting a metal-insulator (M-I) transition at TM-I=63 K were studied by inelastic neutron scattering experiment. The spectra at temperatures much lower than TM-I are described as well-defined crystal-field excitations. With approaching TM-I, the excitation peaks broaden and shift considerably together with the temperature variation of the carrier number and the atomic displacement in the transition. The 4f electron states evolve from the well-localized state in the insulator phase to the strongly hybridized itinerant state by p-f mixing near TM-I. The hybridization is responsible for the M-I transition of PrRu4P12., AMERICAN PHYSICAL SOC
Physical Review B, 2005年
Powder neutron diffraction studies of structure and magnetic Ce ordering in the strongly correlated electron compound Ce0.75La0.2511B6P. Fischer; K. Iwasa; K. Kuwahara; M. Kohgi; T. Hansen and S. Kunii, By means of powder neutron diffraction investigations, chemical structure and magnetic Ce ordering of (Ce0.75La0.25B6)-B-11 have been investigated at temperatures down to 105 mK. In the antiferromagnetic low-temperature phase III (Ce0.75La0.25B6)-B-11 resembles pure CeB6, but has a lower Neel temperature T-N between 0.89 and 1.25 K. Similar to the recently determined magnetic ordering in pure CeB6 (model C), one obtains the compared to CeB6 smaller ordered magnetic Ce moments mu(Ce(1))=0.53(1) mu(B) at z=0 and mu(Ce(2))=0.12(1) mu(B) at z=1/2 with respect to the magnetic unit cell at 105 mK. Presumably this magnetic ordering, which is characterized by both propagation vectors k=[1/4,1/4,0] and k'=[1/4,1/4,1/2], is caused by competition between magnetic dipole and multipolar ordering. At 0.89 K the magnetic moments are reduced to mu(Ce(1))=0.31(1)mu(B) and mu(Ce(2))=0.08(1)mu(B). At 1.25 K in phase IV with presumably multipolar Ce ordering no significant magnetic Bragg peaks associated with magnetic dipole Ce moments were observed, supporting the octupole model of Kubo and Kuramoto for this phase., AMER PHYSICAL SOC
Physical Review B, 2005年
Study of High-field Magnetic Phases of the low-carrier-system CeP by Synchrotron Radiation X-ray DiffractionA. Hanan; D. Kawana; K. Kuwahara; M. Kohgi; Y. Narumi; Y. Tabata; S. Shimomura; Y. Tanaka and K. Katsumata, The magnetic structures of the low-carrier-system CeP are investigated under magnetic fields up to 12.5 T with the field H parallel to [1 (1) over bar0] and up to 14 T with H II [001] by synchrotron X-ray diffraction utilizing the unique relationship between the magnetic structure and lattice modulation in this system. The magnetic phases corresponding to the modulation wave vectors k = 2/11, 2/10, 2/9 and 2/8 are observed at low temperatures, The magnetic phases with k = 2/8 (up arrow up arrow oooooo or up arrow up arrow --- - -), k = 2/9 (up arrow up arrow ooooooo or up arrow - - -- --) and k = 2/11 (up arrow up arrow ooooooooo) are the new phases under magnetic fields found in the present work. The result demonstrates that magnetic fields play a role similar to high pressure to realize the unique magnetic structure and its multistep change in CeP. This fact indicates the importance of the magnetic polaron effect mediated by the p-f mixing effect in the system., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2005年
Role of p-f Hybridization in the Metal-Non-Metal Transition of PrRu4P12K. Iwasa; L. Hao; T. Hasegawa; T. Takagi; K. Horiuchi; Y. Mori; Y. Murakami; K. Kuwahara; M. Kohgi; H. Sugawara; S.R. Saha; Y. Aoki and H. Sato, Electronic state evolution in the metal-nonmetal transition of PrRu4P12 has been studied by X-ray and polarized neutron diffraction experiments. It has been revealed that, in the low-temperature nonmetallic phase, two inequivalent crystal-field (CF) schemes of Pr3+ 4f(2) electrons with Gamma(1) and Gamma((2))(4)-ground states are located at Pr1 and Pr2 sites forming the bee unit cell surrounded by the smaller and larger cubic Ruion sublattices, respectively. This modulated electronic state can be explained by the p-f hybridization mechanism taking two intermediate states of 4f(1) and 4f(3). The p-f hybridization effect plays an important role in the electronic energy gain in the metal-nonmetal transition originated from the Fermi surface nesting., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2005年
Resonant and non-resonant x-ray scattering from GdB6K. Kuwahara; R. Yamamoto; M. Kohgi; H. Nakao; K. Ishii; K. Iwasa; Y. Murakami; S. Kunii; H. Sagayama; Y. Wakabayashi and H. Sawa, We have performed resonant and non-resonant X-ray scattering on GdB6 to investigate the two successive phase transitions at T-N =similar to 15K and T* =similar to 10 K. Below T-N, new superlattice reflection at the wave vector [1/4 1/4 1/2], which is the same wave vector determined by the epithermal neutron diffraction, has been observed by X-ray scattering. In the temperature region between T* and T-N, it was confirmed by the polarization analyses that the superlattice reflection is due to magnetic X-ray scattering. On the other hand, interestingly, the superlattice reflection below T* is mainly due to Thomson scattering. Unlike behavior expected from usual magnetoelastic effects, the wave vector of the lattice distortion is identical to that of the magnetic structure below P. (c) 2005 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2005年
Magnetic Excitations in the Heavy-Fermion Superconductor PrOs4Sb12K. Kuwahara; K. Iwasa; M. Kohgi; K. Kaneko; S. Araki; N. Metoki; H. Sugawara; Y. Aoki and H. Sato, Magnetic excitations in a single crystal of heavy-fermion superconductor PrOs4Sb12 have been studied by inelastic neutron scattering (INS) at low temperatures under high magnetic fields. The crystal field (CF) excitations at 0.7 meV observed in a previous INS study of a polycrystal sample were confirmed in this study on a single crystal. The observed excitations in the zero magnetic field soften around a wave vector (1,0,0), which is the modulation vector of the field-induced antiferro-quadrupolar ordering, suggesting the presence of quadrupolar instability. The observed field dependence of excitations is better reproduced in a singlet ground-state model rather than in a non-Kramers doublet ground-state model. In a high resolution experiment, furthermore, the change of the excitation spectra at (1,0,0) was observed on passing through the superconducting transition temperature, indicating that the excitation and the superconductivity are closely related in PrOs4Sb12., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2004年,
［査読有り］ Neutron-diffraction studies of the unusual ordered phases of Ce0.75La0.25B6K. Iwasa; K. Kuwahara; M. Kohgi; P. Fischer; A. Donni; L. Keller; T. C. Hansen; S. Kunii; N. Metoki and K. Ohyama, Ce0.75La0.25B6 shows paramagnetic phase (phase I), 4f-electron quadrupolar ordered phase (II), magnetically ordered phase (III), and an unknown phase IV. In order to investigate order parameters in phases III and IV, neutron diffraction experiments were performed down to 74 mK. Magnetic diffraction pattern measured in phase III is reproduced by a model in which spin arrangement is modified from the previously suggested structure for CeB6. No magnetic reflections were observed in phase IV. Thus, the order parameter in phase IV is expected to be 4f-electron multipoles rather than magnetic dipoles. (C) 2003 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2003年,
［査読有り］ EXCED - Epithermal neutron diffractometer at KENSK. Kuwahara; S. Sugiyama; K. Iwasa; M. Kohgi; M. Nakamura; Y. Inamura; M. Arai and S. Kunii, A new epithermal neutron diffractometer (EXCED) was installed at the KENS spallation pulsed-neutron source. EXCED is designed to be a small scattering angle diffractometer using an incident neutron energy of about similar to 1 eV for determining the crystal and magnetic structures of materials containing high-absorption elements. Using this diffractometer, we have been able to measure the nuclear and magnetic Bragg peaks of Gd compounds, which are known as the best absorber of thermal neutrons. The instrumental details and the preliminary results of the neutron diffraction from a single crystal of GdB6 are reported., SPRINGER-VERLAG
Applied Physics A, 2002年
Magnetic form factor of UGe2 under high pressureK. Kuwahara; H. Sagayama; K. Iwasa; M. Kohgi; Y. Haga; Y. Onuki; K. Kakurai; M. Nishi; K. Nakajima; N. Aso and Y. Uwatoko, The magnetic form factor in the pressure-induced ferromagnetic superconductor UGe2 has been measured with polarized neutrons. The experiments were performed on single crystal samples at 2 K by applying a magnetic field of 2 T along the easy magnetization axis a under pressures of 0 and 1.4 GPa. In spite of the itinerant nature of the 5f electrons, the shapes of the observed magnetic form factors at both 0 and 1.4 GPa are very close to the theoretical 5f form factor of the free U3+ or U4+ ions calculated by the dipole approximation. The effect of pressure on the 5f form factor seems to be small in spite of the reduction of the magnetic moment. (C) 2002 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2002年
Spatially inhomogeneous development of antiferromagnetism in URu2Si2: Evidence from 29Si NMR under pressureK. Mastuda; Y. Kohori; T. Kohara; K. Kuwahara and H. Amitsuka, From Si-29 NMR study, we present evidence for spatially inhomogeneous development of antiferromagnetic (AF) ordering below T-o = 17.5 K in URu2Si2. In the pressure range between 3.0 and 8.3 kbar. we have observed the Si-29 NMR lines arising from the AF region as well as the previously observed Si-29 NMR line which correspond to the nonmagnetic region in the sample. The AF volume fraction is enhanced by applied pressure, whereas the magnitude of internal field at the Si site remains constant (910 Oe) up to 8.3 kbar. In the AF region, the ordered moment is about an order of magnitude larger than 0.03 mu (B)/U., AMER PHYSICAL SOC
Physical Review Letters, 2001年,
［査読有り］ Effect of pressure on tiny antiferromagnetic moment in the heavy-electron compound URu(2)Si(2)H Amitsuka; M Sato; N Metoki; M Yokoyama; K Kuwahara; T Sakakibara; H Morimoto; S Kawarazaki; Y Miyako; JA Mydosh, We have performed elastic neutron-scattering experiments on the heavy-electron compound URu(2)Si(2) for pressure P up to 2.8 GPa. We have found that the antiferromagnetic (100) Bragg reflection below T(m) similar to 17.5 K is strongly enhanced by applying pressure. For P < 1.1 GPa, the staggered moment mu(0) at 1.4 K increases linearly from similar to 0.017(3)mu(B) to similar to 0.25(2)mu(B), while T(m) increases slightly at a rate similar to 1 K/GPa, roughly following the transition temperature T(0) determined from macroscopic anomalies. We have also observed a sharp phase transition at P(0) similar to 1.5 GPa, above which a 3D-Ising type of antiferromagnetic phase (mu(0) similar to 0.4 mu(B)) appears with a slightly reduced lattice constant., AMER PHYSICAL SOC
PHYSICAL REVIEW LETTERS, 1999年12月,
［査読有り］ Lattice instability and elastic responce in the heavy electron system URu2Si2K. Kuwahara; H. Amitsuka; T. Sakakibara; O. Suzuki; S. Nakamura; T. Goto; M. Mihalik; A.A. Menovsky; A. de Visser and J.J.M. Franse, We have performed thermal expansion and elastic constant measurements of the heavy electron system URu2Si2, focusing attention on the Gamma(3)(x(2) - y(2)) and Gamma(4)(xy) symmetry of the tetragonal group D-4h. It is reconfirmed that there is no sizable uniform spontaneous distortion for these two types of symmetry through the puzzling phase transition at T-o = 17.5 K. On the other hand, a weak but significant tendency of softening are found below about 70 K in the transverse (C-11 - C-12)/2 mode. The results strongly suggest the presence of a lattice instability in the Gamma 3 symmetry. From the results, proposed crystalline-electric-field models are also discussed., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 1997年,
［査読有り］
