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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

 Times Cited Count:14 Percentile:67.34(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

Anomalous metallic state in the vicinity of metal to valence-bond solid insulator transition in LiVS$$_{2}$$

Katayama, Naoyuki*; Uchida, Masaya*; Hashizume, Daisuke*; Niitaka, Seiji*; Matsuno, Jobu*; Matsumura, Daiju; Nishihata, Yasuo; Mizuki, Junichiro; Takeshita, Nao*; Gauzzi, A.*; et al.

Physical Review Letters, 103(14), p.146405_1 - 146405_4, 2009/10

 Times Cited Count:55 Percentile:88.29(Physics, Multidisciplinary)

We investigate LiVS$$_{2}$$ and LiVSe$$_{2}$$ with a triangular lattice as itinerant analogues of LiVO$$_{2}$$ known for the formation of a valence-bond solid (VBS) state out of an S = 1 frustrated magnet. LiVS$$_{2}$$, which is located at the border between a metal and a correlated insulator, shows a first order transition from a paramagnetic metal to a VBS insulator at T$$_{c}$$ $$sim$$ 305 K upon cooling. The presence of a VBS state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in the formation of a VBS state. We argue that the high temperature metallic phase of LiVS$$_{2}$$ has a pseudogap, likely originating from the VBS fluctuation. LiVSe$$_{2}$$ was found to be a paramagnetic metal down to 2 K.

Journal Articles

Neutron powder diffraction study on the crystal and magnetic structures of BiCoO$$_3$$

Belik, A. A.*; Iikubo, Satoshi; Kodama, Katsuaki; Igawa, Naoki; Shamoto, Shinichi; Niitaka, Seiji*; Azuma, Masaki*; Shimakawa, Yuichi*; Takano, Mikio*; Izumi, Fujio*; et al.

Chemistry of Materials, 18(3), p.798 - 803, 2006/02

 Times Cited Count:272 Percentile:98.63(Chemistry, Physical)

The crystal and magnetic structures of polycrystalline BiCoO$$_3$$ have been determined by the Rietveldmethod from neutron diffraction data measured at temperatures from 5 to 520 K. BiCoO$$_3$$ (space groupP4mm; Z=1; a=3.72937(7) ${AA}$ and c=4.72382(15) ${AA}$ at room temperature; tetragonality c/a=1.267) is isotypic with BaTiO$$_3$$ and PbTiO$$_3$$ in the whole temperature range. BiCoO$$_3$$ is an insulator with a Neeltemperature of 470 K. A possible model for antiferromagnetic order is proposed with a propagationvector of k=(1/2, 1/2, 0). In this model, magnetic moments of Co$$^{3+}$$ ions are parallel to the c directionand align antiferromagnetically in the ab plane. The antiferromagnetic ab layers stack ferromagneticallyalong the c axis, forming a C-type antiferromagnetic structure. Refined magnetic moments at 5 and 300K are 3.24(2)$$mu$$$$_B$$ and 2.93(2)$$mu$$$$_B$$, respectively. The structure refinements revealed no deviation fromstoichiometry in BiCoO$$_3$$. BiCoO$$_3$$ decomposed in air above 720 K to give Co$$_3$$O$$_4$$ and sillenite-like Bi$$_{25}$$CoO$$_{39}$$.

Journal Articles

Synthesis of materials under high pressure by means of synchrotron X-ray diffraction

Azuma, Masaki*; Saito, Takashi*; Niitaka, Seiji*; Ishiwata, Shintaro*; Kanda, Hiroaki*; Yamada, Ikuya*; Takano, Mikio*; Utsumi, Wataru

Kotai Butsuri, 38(2), p.141 - 150, 2003/02

no abstracts in English

Journal Articles

Partially disordered antiferromagnetic phase in Ca$$_{3}$$CoRhO$$_{6}$$

Niitaka, Seiji*; Yoshimura, Kazuyoshi*; Kosuge, K.*; Nishi, Masakazu*; Kakurai, Kazuhisa

Physical Review Letters, 87(17), p.177202_1 - 177202_4, 2001/10

 Times Cited Count:95 Percentile:91.65(Physics, Multidisciplinary)

no abstracts in English

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