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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

Weyl-Kondo semimetal behavior in the chiral structure phase of Ce$$_{3}$$Rh$$_{4}$$Sn$$_{13}$$

Iwasa, Kazuaki*; Suyama, Kazuya*; Kawamura, Seiko; Nakajima, Kenji; Raymond, S.*; Steffens, P.*; Yamada, Akira*; Matsuda, Tatsuma*; Aoki, Yuji*; Kawasaki, Ikuto; et al.

Physical Review Materials (Internet), 7(1), p.014201_1 - 014201_11, 2023/01

https://doi.org/10.1103/PhysRevMaterials.7.014201
 Times Cited Count：2 Percentile：72.03(Materials Science, Multidisciplinary)

Journal Articles

Multipole polaron in the devil's staircase of CeSb

Arai, Yosuke*; Kuroda, Kenta*; Nomoto, Takuya*; Tin, Z. H.*; Sakuragi, Shunsuke*; Bareille, C.*; Akebi, Shuntaro*; Kurokawa, Kifu*; Kinoshita, Yuto*; Zhang, W.-L.*; et al.

Nature Materials, 21(4), p.410 - 415, 2022/04

https://doi.org/10.1038/s41563-021-01188-9
 Times Cited Count：7 Percentile：77.62(Chemistry, Physical)

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

Quantum paramagnet near spin-state transition

Tomiyasu, Keisuke*; Ito, Naoko*; Okazaki, Ryuji*; Takahashi, Yuki*; Onodera, Mitsugi*; Iwasa, Kazuaki*; Nojima, Tsutomu*; Aoyama, Takuya*; Ogushi, Kenya*; Ishikawa, Yoshihisa*; et al.

Advanced Quantum Technologies (Internet), 1(3), p.1800057_1 - 1800057_7, 2018/12

https://doi.org/10.1002/qute.201800057

Spin-state transition, also known as spin crossover, plays a key role in diverse systems. In theory, the boundary range between the low- and high-spin states is expected to enrich the transition and give rise to unusual physical states. However, no compound that realizes a nearly degenerate critical range as the ground state without requiring special external conditions has yet been experimentally identified. This study reports that the Sc substitution in LaCoO3 destabilizes its nonmagnetic low-spin state and generates an anomalous paramagnetic state accompanied by the enhancement of transport gap and magneto-lattice-expansion as well as the contraction of Co-O distance with the increase of electron site transfer. These phenomena are not well described by the mixture of conventional low- and high-spin states, but by their quantum superposition occurring on the verge of a spin-state transition.

Journal Articles

Magnetic-ordering propagation vectors of terbium hexaboride revisited

Iwasa, Kazuaki*; Iga, Fumitoshi*; Moyoshi, Taketo*; Nakao, Akiko*; Ohara, Takashi

Journal of the Physical Society of Japan, 87(6), p.064705_1 - 064705_5, 2018/06

https://doi.org/10.7566/JPSJ.87.064705
 Times Cited Count：0 Percentile：0(Physics, Multidisciplinary)

Journal Articles

Magnetic properties of electron-doped LaCoO$$_3$$

Tomiyasu, Keisuke*; Sato, Mika*; Koyama, Shunichi*; Nojima, Tsutomu*; Kajimoto, Ryoichi; Ji, S.*; Iwasa, Kazuaki*

Journal of the Physical Society of Japan, 86(9), p.094706_1 - 094706_6, 2017/09

https://doi.org/10.7566/JPSJ.86.094706
 Times Cited Count：4 Percentile：35.79(Physics, Multidisciplinary)

Journal Articles

Second-order structural transition in the superconductor La$$_3$$Co$$_4$$Sn$$_{13}$$

Cheung, Y. W.*; Zhang, J. Z.*; Zhu, J. Y.*; Yu, W. C.*; Hu, Y. J.*; Wang, D. G.*; Otomo, Yuka*; Iwasa, Kazuaki*; Kaneko, Koji; Imai, Masaki*; et al.

Physical Review B, 93(24), p.241112_1 - 241112_5, 2016/06

AA2016-0058.pdf:0.95MB

https://doi.org/10.1103/PhysRevB.93.241112
 Times Cited Count：14 Percentile：54.92(Materials Science, Multidisciplinary)

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

Spin-orbit fluctuations in frustrated heavy-fermion metal LiV$$_{2}$$O$$_{4}$$

Tomiyasu, Keisuke*; Iwasa, Kazuaki*; Ueda, Hiroaki*; Niitaka, Seiji*; Takagi, Hidenori*; Kawamura, Seiko; Kikuchi, Tatsuya; Inamura, Yasuhiro; Nakajima, Kenji; Yamada, Kazuyoshi*

Physical Review Letters, 113(23), p.236402_1 - 236402_5, 2014/12

https://doi.org/10.1103/PhysRevLett.113.236402
 Times Cited Count：16 Percentile：68.53(Physics, Multidisciplinary)

Spin fluctuations were studied over a wide momentum ($$hbar$$$$Q$$) and energy ($$E$$) space in the frustrated ${it d}$-electron heavy-fermion metal LiV$$_{2}$$O$$_{4}$$ by time-of-flight inelastic neutron scattering. We observed the overall ${it Q-E}$ evolutions near the characteristic ${it Q}$ = 0.6 $AA $^{-1}$$ peak and found another weak broad magnetic peak around 2.4 $AA $^{-1}$$. The data are described by a simple response function, a partially delocalized magnetic form factor, and antiferromagnetic short-range spatial correlations, indicating that heavy-fermion formation is attributable to spin-orbit fluctuations with orbital hybridization.

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

Magnetic phase diagrams of YVO$$_{3}$$ and TbVO$$_{3}$$ under high pressure

Bizen, Daisuke*; Nakao, Hironori*; Iwasa, Kazuaki*; Murakami, Yoichi*; Osakabe, Toyotaka; Fujioka, Jun*; Yasue, Toshio*; Miyasaka, Shigeki*; Tokura, Yoshinori*

Journal of the Physical Society of Japan, 81(2), p.024715_1 - 024715_6, 2012/02

https://doi.org/10.1143/JPSJ.81.024715
 Times Cited Count：6 Percentile：42.8(Physics, Multidisciplinary)

The magnetic phase diagrams for $$R$$VO$$_{3}$$ ($$R$$ = Y, Tb) were determined by low temperature and high pressure neutron-diffraction techniques. We found that the magnetic ground state in TbVO$$_{3}$$ changes from ${it C}$-type spin ordering (${it C}$-SO) to ${it G}$-type spin ordering (${it G}$-SO) on application of pressure. The transition of the magnetic ground state also indicates that the ground state of the orbital ordering changes from ${it G}$-type orbital ordering (${it G}$-OO) to ${it C}$-type orbital ordering (${it C}$-OO). In YVO$$_{3}$$, the ${it G}$-SO and ${it C}$-OO phases set in simultaneously up to 6.2 GPa, and the disorder-[${it G}$-SO, ${it C}$-OO] phase transition appears above 6 GPa. This is the first observation of a simultaneous spin and orbital order-disorder phase transition in perovskite-type transition-metal oxides $$R$$MO$$_{3}$$. The [${it G}$-SO, ${it C}$-OO] phase is strongly stabilized with increasing pressure, and both the covalency effect and the superexchange interaction play roles in this stabilization.

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

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

Fractal dimension in percolating Heisenberg antiferromagnets

Ito, Shinichi*; Kajimoto, Ryoichi; Adams, M. A.*; Bull, M. J.*; Iwasa, Kazuaki*; Aso, Naofumi*; Yoshizawa, Hideki*; Takeuchi, Tetsuya*

Journal of Magnetism and Magnetic Materials, 310(2, Part2), p.1549 - 1551, 2007/03

We investigated static and dynamical properties in the three-dimensional percolating Heisenberg antiferromagnets, RbMn$$_c$$Mg$$_{1-c}$$F$$_3$$, with the magnetic concentration close to the percolation threshold, $$c_P = 0.312$$, around the superlattice point well below $$T_N$$. In neutron diffraction experiment, the wave number dependence of the elastic scattering component was well fitted to $$q^{-x}$$. Magnetic fractons were also studied using inelastic neutron scattering, and the observed fractons showed the dispersion relation of $$q^z$$. The determined exponents, $$x = 2.43 pm 0.05$$ and $$z = 2.5 pm 0.1$$, were in good agreement with the fractal dimension ($$D_f = 2.48$$).

Journal Articles

Resonant X-ray scattering of PrRu$$_4$$P$$_{12}$$

Ishii, Kenji; Tsutsui, Satoshi*; Hao, L.*; Hasegawa, Tomoo*; Iwasa, Kazuaki*; Tsubota, Masami; Inami, Toshiya; Murakami, Yoichi*; Saha, S. R.*; Sugawara, Hitoshi*; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.e178 - e180, 2007/03

PrRu$$_4$$P$$_{12}$$ shows a metal-insulator (MI) transition at $$T_{mathrm MI} simeq$$ 62 K accompanied by a structural phase transition. Because LaRu$$_4$$P$$_{12}$$ without $$4f$$ electrons does not shows the MI transition, $$4f$$ electrons in the Pr atom plays an important role in the transition. In order to elucidate a modulation of electronic states of Pr, we have carried out a resonant X-ray scattering study of PrRu$$_4$$P$$_{12}$$ at Pr $$L_2$$- and $$L_3$$-edges. Below $$T_{mathrm MI}$$, resonant signal at the absorption main-edge was successfully observed at the superlattice reflections of the modulation vector $$vec{q}=(1,0,0)$$ in addition to the energy-independent component from the lattice distortion. Because the reflection contains the difference of anomalous scattering factors between two Pr atoms in the unit cell, two different electronic states are actually ordered below $$T_{MI}$$. Furthermore we found that the polarization of X-ray is mostly unrotated even at the resonance, which indicates that the resonant scattering in PrRu$$_4$$P$$_{12}$$ is almost isotropic.

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

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.

41 (Records 1-20 displayed on this page)