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Journal Articles

Magnetic ordering and structural phase transitions of Nd$$_{3}$$$$T$$$$_{4}$$Sn$$_{13}$$ ($$T$$ = Rh and Ir)

Shimoda, Ami*; Iwasa, Kazuaki*; Kuwahara, Keitaro*; Sagayama, Hajime*; Nakao, Hironori*; Ishikado, Motoyuki*; Ohara, Takashi; Nakao, Akiko*; Hoshikawa, Akinori*; Ishigaki, Toru*

JPS Conference Proceedings (Internet), 38, p.011091_1 - 011091_6, 2023/05

https://doi.org/10.7566/JPSCP.38.011091

Journal Articles

Gaps in topological magnon spectra; Intrinsic versus extrinsic effects

Do, S.-H.*; Paddison, J. A. M.*; Sala, G.*; Williams, T. J.*; Kaneko, Koji; Kuwahara, Keitaro*; May, A. F.*; Yan, J.*; McGuire, M. A.*; Stone, M. B.*; et al.

Physical Review B, 106(6), p.L060408_1 - L060408_6, 2022/08

https://doi.org/10.1103/PhysRevB.106.L060408
 Times Cited Count：10 Percentile：83.82(Materials Science, Multidisciplinary)

Journal Articles

Successive phase transitions in $$R_{3}$$Ir$$_{4}$$Sn$$_{13}$$ ($$R$$: La and Ce) investigated using neutron and X-ray diffraction

Nakazato, Seiya*; Iwasa, Kazuaki*; Hashimoto, Daisuke*; Shiozawa, Mami*; Kuwahara, Keitaro*; Nakao, Hironori*; Sagayama, Hajime*; Ishikado, Motoyuki*; Ohara, Takashi; Nakao, Akiko*; et al.

JPS Conference Proceedings (Internet), 30, p.011128_1 - 011128_6, 2020/03

https://doi.org/10.7566/JPSCP.30.011128

Journal Articles

Structure of the magnetic excitations in the spin-1/2 triangular-lattice Heisenberg antiferromagnet Ba$$_{3}$$CoSb$$_{2}$$O$$_{9}$$

Ito, Saya*; Kurita, Nubuyuki*; Tanaka, Hidekazu*; Kawamura, Seiko; Nakajima, Kenji; Ito, Shinichi*; Kuwahara, Keitaro*; Kakurai, Kazuhisa*

Nature Communications (Internet), 8, p.235_1 - 235_6, 2017/08

https://doi.org/10.1038/s41467-017-00316-x
 Times Cited Count：76 Percentile：93.89(Multidisciplinary Sciences)

Journal Articles

Science from the initial operation of HRC

Ito, Shinichi*; Yokoo, Tetsuya*; Masuda, Takatsugu*; Yoshizawa, Hideki*; Soda, Minoru*; Ikeda, Yoichi*; Ibuka, Soshi*; Kawana, Daichi*; Sato, Taku*; Nambu, Yusuke*; et al.

JPS Conference Proceedings (Internet), 8, p.034001_1 - 034001_6, 2015/09

https://doi.org/10.7566/JPSCP.8.034001

Journal Articles

Development of technique for electrical insulation of metallic gasket using anodic oxide coating

Osakabe, Toyotaka; Kato, Yoshihiro*; Honmoto, Satoru*; Kuwahara, Keitaro*

Koatsuryoku No Kagaku To Gijutsu, 25(1), p.57 - 63, 2015/03

https://doi.org/10.4131/jshpreview.25.57

In this article, we describe an unique technique for electrical insulation of metallic gasket to perform simultaneous measurements of electrical resistivity and neutron diffraction under high pressure. The anodic oxide coating was adopted as the insulation layer of the aluminum (JIS A2017) gasket used in the hybrid-anvil device for neutron diffraction. In the feasibility tests of the coated gaskets, maximum pressure of about 6 GPa was generated without electrical breakdown of the coating or disconnection of Au leads.

Journal Articles

Magnetic excitation in totally symmetric staggered ordered phase of PrFe$$_4$$P$$_{12}$$

Iwasa, Kazuaki*; Hao, L.*; Kogi, Masafumi*; Kuwahara, Keitaro*; Mignot, J.-M.*; Sugawara, Hitoshi*; Aoki, Yuji*; Matsuda, Tatsuma; Sato, Hideyuki*

Journal of the Physical Society of Japan, 81(9), p.094711_1 - 094711_9, 2012/09

https://doi.org/10.1143/JPSJ.81.094711
 Times Cited Count：9 Percentile：52.9(Physics, Multidisciplinary)

Journal Articles

Pressure-induced antiferromagnetic order in filled skutterudite PrFe$$_{4}$$P$$_{12}$$ studied by single-crystal high-pressure neutron diffraction

Osakabe, Toyotaka; Kuwahara, Keitaro*; Kawana, Daichi*; Iwasa, Kazuaki*; Kikuchi, Daisuke*; Aoki, Yuji*; Kogi, Masafumi*; Sato, Hideyuki*

Journal of the Physical Society of Japan, 79(3), p.034711_1 - 034711_7, 2010/03

https://doi.org/10.1143/JPSJ.79.034711
 Times Cited Count：18 Percentile：68.73(Physics, Multidisciplinary)

Journal Articles

Unusual electronic state of the low-carrier system CeSb under high pressure studied by simultaneous measurement of electrical resistivity and lattice parameter

Hannan, A.*; Okayama, Yasushi*; Osakabe, Toyotaka; Kuwahara, Keitaro*; Kogi, Masafumi*

Journal of the Physical Society of Japan, 76(5), p.054706_1 - 054706_6, 2007/05

https://doi.org/10.1143/JPSJ.76.054706
 Times Cited Count：1 Percentile：10.86(Physics, Multidisciplinary)

We have studied the origin of the anomalous peak structure of resistivity of the low-carrier system CeSb appeared around the antiferromagnetic transition temperature T$$_{N}$$ under high pressures by means of simultaneous measurement of lattice parameter by X-ray diffraction and resistivity together with neutron diffraction technique. It was found that there is a strong relationship between the unusual decrease of lattice parameter and the unusual increase of resistance below T$$_{N}$$ under high pressure. Both of these phenomena can be explained by the appearance of the $$Gamma$$$$_{8}$$ - like magnetic state of Ce$$^{3+}$$ ion below T$$_{N}$$.

Journal Articles

The Unconventional superconductivity of skutterudite PrOs$$_4$$Sb$$_{12}$$; Time-reversal symmetry breaking and adjacent field-induced quadrupole ordering

Aoki, Yuji*; Tayama, Takashi*; Sakakibara, Toshiro*; Kuwahara, Keitaro*; Iwasa, Kazuaki*; Kogi, Masafumi*; Higemoto, Wataru; MacLaughlin, D. E.*; Sugawara, Hitoshi*; Sato, Hideyuki*

Journal of the Physical Society of Japan, 76(5), p.051006_1 - 051006_13, 2007/05

https://doi.org/10.1143/JPSJ.76.051006
 Times Cited Count：63 Percentile：57.04(Physics, Multidisciplinary)

This review presents a summary and evaluation of the experimental properties of unconventional superconductivity in PrOs$$_4$$Sb$$_{12}$$. After a brief introduction of filled skutterudites, we argue that the normal-state properties of PrOs$$_4$$Sb$$_{12}$$ are quite different from ordinary heavy-fermion superconductors.

Journal Articles

Development of a hybrid-anvil type high-pressure device and its application to magnetic neutron scattering studies

Osakabe, Toyotaka; Kakurai, Kazuhisa; Kawana, Daichi*; Kuwahara, Keitaro*

Journal of Magnetism and Magnetic Materials, 310(2, Part3), p.2725 - 2727, 2007/03

no abstracts in English

Journal Articles

Elastic anomalies of UGe$$_2$$

Kuwahara, Keitaro*; Sakai, Takashi*; Kogi, Masafumi*; Haga, Yoshinori; Onuki, Yoshichika

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.362 - 364, 2007/03

We have performed the ultrasonic sound velocity measurement on the single crystal of UGe$$_2$$ in the temperature range 4-120 K at ambient pressure, focusing attention on the elastic behavior around the characteristic temperature $$T^{*}$$ = 30 K. In the elastic constants forthree 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 wasobserved around $$T^{*}$$ in the transverse $$c$$$$_{55}$$ and $$c$$$$_{66}$$ modes.

Journal Articles

Neutron scattering study on the field-induced $$O_{xy}$$-type antiferroquadrupolar ordering of the heavy-fermion superconductor PrOs$$_4$$Sb$$_{12}$$

Kaneko, Koji; Metoki, Naoto; Shiina, Ryosuke*; Matsuda, Tatsuma; Kogi, Masafumi*; Kuwahara, Keitaro*; Bernhoeft, N.*

Physical Review B, 75(9), p.094408_1 - 094408_7, 2007/03

https://doi.org/10.1103/PhysRevB.75.094408
 Times Cited Count：21 Percentile：64.75(Materials Science, Multidisciplinary)

Neutron scattering experiments have revealed a field-induced antiferroquadrupolar order parameter in the Pr-based heavy-fermion superconductor PrOs$$_4$$Sb$$_{12}$$. We observed the field-induced antiferromagnetic dipole moment with the propagation vector $$q$$ = (1 0 0) for the applied field direction both $$H parallel$$ [1 1 0] and [0 0 1]. For $$H parallel$$ [1 1 0] at 8 T, it should be noted that the induced antiferromagnetic moment of 0.16 $$mu_{rm B}$$/ Pr orients parallel to the field within our experimental accuracy. This observation is strong evidence that the $$O_{xy}$$ electric quadrupole to be the primary order parameter for $$H parallel$$ [1 1 0]. A mean-field calculation, based on $$Gamma_1$$ singlet and $${Gamma}_4^{(2)}$$ 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 PrOs$$_4$$Sb$$_{12}$$.

Journal Articles

Structural transformation on the pressure-induced metal-insulator transition in PrFe$$_{4}$$4P$$_{12}$$

Kawana, Daichi*; Kuwahara, Keitaro*; Sato, Masashi*; Takagi, Masatoshi*; Aoki, Yuji*; Kogi, Masafumi*; Sato, Hideyuki*; Sagayama, Hajime*; Osakabe, Toyotaka; Iwasa, Kazuaki*; et al.

Journal of the Physical Society of Japan, 75(11), p.113602_1 - 113602_4, 2006/11

https://doi.org/10.1143/JPSJ.75.113602
 Times Cited Count：11 Percentile：56.33(Physics, Multidisciplinary)

We report the first X-ray diffraction experiments of PrFe$$_{4}$$P$$_{12}$$ 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.

Journal Articles

Inelastic neutron scattering study on low-energy excitations of the heavy-fermion superconductor PrOs$$_4$$Sb$$_{12}$$

Kuwahara, Keitaro*; Iwasa, Kazuaki*; Kogi, Masafumi*; Kaneko, Koji; Metoki, Naoto; Raymond, S.*; M$'e$asson, M.-A.*; Flouquet, J.*; Sugawara, Hitoshi*; Aoki, Yuji*; et al.

Physica B; Condensed Matter, 385-386(Part 1), p.82 - 84, 2006/11

https://doi.org/10.1016/j.physb.2006.05.109
 Times Cited Count：3 Percentile：17.99(Physics, Condensed Matter)

We report inelastic neutron scattering experiments performed to investigate the low energy magnetic excitations on single crystals of the heavy-fermion superconductor PrOs$$_4$$Sb$$_{12}$$. 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.

Journal Articles

Field-induced antiferroquadrupolar order in the heavy fermion superconductor PrOs$$_4$$Sb$$_{12}$$

Kaneko, Koji; Metoki, Naoto; Matsuda, Tatsuma; Kuwahara, Keitaro*; Kogi, Masafumi*; Shiina, Ryosuke*; Mignot, J.-M.*; Gukasov, A.*; Bernhoeft, N.*

Physica B; Condensed Matter, 378-380, p.189 - 191, 2006/05

https://doi.org/10.1016/j.physb.2006.01.349
 Times Cited Count：1 Percentile：6.64(Physics, Condensed Matter)

Neutron diffraction experiments under magnetic fields were carried out on the heavy fermion superconductor PrOs$$_4$$Sb$$_{12}$$ in order to reveal the origin of the field-induced ordered phase (FIOP) for $$H$$$$Vert$$[1,1,0]. The application of magnetic field induces the weak superlattice peaks with the ordering vector $$q$$=(1,0,0) in FIOP, which is the same as for $$H{parallel}$$[0,0,1]. The observed superlattice reflections for $$H$$$$Vert$$[1,1,0] result from the antiferromagnetic component of $$J_x$$+$$J_y$$; the induced tiny antiferromagnetic moments orient parallel to the applied field. This result cannot be explained by magnetic interactions and strongly evidences the underlying AFQ order with $$O_{xy}$$ as a primary order parameter. These facts clarify the dominant role of $$O_{xy}$$-type antiferroquadrupolar interaction in PrOs$$_4$$Sb$$_{12}$$.

Journal Articles

Direct observation of quadrupolar excitons in the heavy-fermion superconductor PrOs$$_4$$Sb$$_12$$

Kuwahara, Keitaro*; Iwasa, Kazuaki*; Kogi, Masafumi*; Kaneko, Koji; Metoki, Naoto; Raymond, S.*; M$'e$asson, M.-A.*; Flouquet, J.*; Sugawara, Hitoshi*; Aoki, Yuji*; et al.

Physical Review Letters, 95(10), p.107003_1 - 107003_4, 2005/09

https://doi.org/10.1103/PhysRevLett.95.107003
 Times Cited Count：96 Percentile：92.15(Physics, Multidisciplinary)

We report inelastic neutron scattering experiments performed to investigate the low energy magnetic excitations on single crystals of the heavy-fermion superconductor PrOs$$_4$$Sb$$_{12}$$. 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.

Journal Articles

Magnetic excitations in the heavy-fermion superconductor PrOs$$_4$$Sb$$_{12}$$

Raymond, S.*; Flouquet, J.*; Kuwahara, Keitaro*; Iwasa, Kazuaki*; Kogi, Masafumi*; Kaneko, Koji; Metoki, Naoto; Sugawara, Hitoshi*; Aoki, Yuji*; Sato, Hideyuki*

Physica B; Condensed Matter, 359-361, p.898 - 900, 2005/06

https://doi.org/10.1016/j.physb.2005.01.256
 Times Cited Count：2 Percentile：11.66(Physics, Condensed Matter)

The low lying magnetic excitations of the unconventional heavy fermion superconductor PrOs$$_4$$Sb$$_{12}$$ were studied by inelastic neutron scattering on single crystalline sample. The crystal field excitation first evidenced at 0.7 meV on powder samples is found to have a minimum of energy at the zone boundary corresponding to the wavevector of antiferro-quadrupolar instability. The evolution of the magnetic excitation spectrum under magnetic field confirms the singlet ground state.

Journal Articles

Electrical and magnetic properties of a single crystal UCu$$_2$$Si$$_2$$

Matsuda, Tatsuma; Haga, Yoshinori; Ikeda, Shugo; Galatanu, A.; Yamamoto, Etsuji; Shishido, Hiroaki*; Yamada, Mineko*; Yamaura, Junichi*; Hedo, Masato*; Uwatoko, Yoshiya*; et al.

Journal of the Physical Society of Japan, 74(5), p.1552 - 1556, 2005/05

https://doi.org/10.1143/JPSJ.74.1552
 Times Cited Count：24 Percentile：72.16(Physics, Multidisciplinary)

We have succeeded in growing a high-quality single crystal of UCu$$_2$$Si$$_2$$ with the tetragonal structure by the Sn-flux method and measured the electrical resistivity, magnetic susceptibility, magnetization and specific heat. UCu$$_2$$Si$$_2$$ is found to order antiferromagnetically below $$T_{rm N}$$ = 106 K, and follows a successive ferromagnetic ordering at $$T_{rm C}$$ = 100 K. The magnetic properties are highly anisotropic, reflecting the crystal structure. An easy-axis of magnetization is found to be the [001] direction ($$c$$-axis) both in the antiferromagnetic and ferromagnetic phases, while the [100] direction ($$a$$-axis) corresponds to the hard-axis in magnetization. The magnetization curve in the antiferromagnetic phase indicates a clear metamagnetic transition at a low field of about 1 kOe and changes smoothly into a ferromagnetic magnetization curve below $$T_{rm C}$$ = 100 K. The saturation moment is determined as 1.75$$mu_{rm B}$$/U at 2 K. The electronic specific heat coefficient is also determined as 20 mJ/K$$^2$$$$cdot$$mol.

Journal Articles

Magnetic excitations in heavy-fermion superconductor PrOs$$_{4}$$Sb$$_{12}$$

Kuwahara, Keitaro*; Iwasa, Kazuaki*; Kogi, Masafumi*; Kaneko, Koji; Araki, Shingo; Metoki, Naoto; Sugawara, Hitoshi*; Aoki, Yuji*; Sato, Hideyuki*

Journal of the Physical Society of Japan, 73(6), p.1438 - 1441, 2004/06

https://doi.org/10.1143/JPSJ.73.1438
 Times Cited Count：64 Percentile：87.39(Physics, Multidisciplinary)

no abstracts in English

39 (Records 1-20 displayed on this page)