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Journal Articles

Emergent spin-1 Haldane gap and ferroelectricity in a frustrated spin-$$frac{1}{2}$$ ladder

Ueda, Hiroshi*; Onoda, Shigeki*; Yamaguchi, Yasuhiro*; Kimura, Tsuyoshi*; Yoshizawa, Daichi*; Morioka, Toshiaki*; Hagiwara, Masayuki*; Hagihara, Masato*; Soda, Minoru*; Masuda, Takatsugu*; et al.

Physical Review B, 101(14), p.140408_1 - 140408_6, 2020/04

 Times Cited Count:3 Percentile:27.19(Materials Science, Multidisciplinary)

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

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 properties of one-dimensional quantum spin system Rb$$_2$$Cu$$_2$$Mo$$_3$$O$$_{12}$$ studied by muon spin relaxation

Kawamura, Seiko; Tomiyasu, Keisuke*; Koda, Akihiro*; Sari, D. P.*; Asih, R.*; Yoon, S.*; Watanabe, Isao*; Nakajima, Kenji

JPS Conference Proceedings (Internet), 21, p.011007_1 - 011007_5, 2018/03

Rb$$_2$$Cu$$_2$$Mo$$_3$$O$$_{12}$$ is a one-dimensional quantum spin system with spin frustration. The magnetic ground state of this system has been expected to be incommensurate spin-singlet from a theoretical study. Furthermore, it was recently reported that this system exhibited ferroelectricity under a magnetic field. We carried out $$mu$$SR studies on this system to understand the magnetic properties. A slow muon spin relaxation due to nuclear dipoles is observed in the whole measured temperatures ranging from 0.06 K to 250 K, indicating that no magnetic ordering. The result suggests that the system shows a spin-singlet ground state. Furthermore, it was found that the distribution of the internal magnetic field were slightly enhanced below 10 K. This temperature dependence resembles that of the electric polarization observed in the magnetic field. It may indicate that some local anomaly of charge/spin related to the ferroelectricity is detected by a microscopic probe.

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

 Times Cited Count:4 Percentile:36.07(Physics, Multidisciplinary)

Journal Articles

Observation of all-in type tetrahedral displacements in nonmagnetic pyrochlore niobates

Torigoe, Shuhei*; Ishimoto, Yutaro*; Aoishi, Yuhei*; Murakawa, Hiroshi*; Matsumura, Daiju; Yoshii, Kenji; Yoneda, Yasuhiro; Nishihata, Yasuo; Kodama, Katsuaki; Tomiyasu, Keisuke*; et al.

Physical Review B, 93(8), p.085109_1 - 085109_5, 2016/02

 Times Cited Count:5 Percentile:26.09(Materials Science, Multidisciplinary)

Journal Articles

Development of spin correlations in the geometrically frustrated triangular-lattice Heisenberg antiferromagnet CuCrO$$_2$$

Kajimoto, Ryoichi; Tomiyasu, Keisuke*; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Okuda, Tetsuji*

Journal of the Physical Society of Japan, 84(7), p.074708_1 - 074708_6, 2015/07

 Times Cited Count:9 Percentile:56.08(Physics, Multidisciplinary)

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

Low-energy spin fluctuations in CuCrO$$_{2}$$ and Cu$$_{0.85}$$Ag$$_{0.15}$$CrO$$_{2}$$ studied by inelastic neutron scattering

Kajimoto, Ryoichi; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Okuda, Tetsuji*; Tomiyasu, Keisuke*

JPS Conference Proceedings (Internet), 3, p.014018_1 - 014018_5, 2014/06

Journal Articles

Magnetic excitations in infinite-layer antiferromagnetic insulator

Tomiyasu, Keisuke*; Kageyama, Hiroshi*; Lee, C.*; Whangbo, M. H.*; Tsujimoto, Yoshihiro*; Yoshimura, Kazuyoshi*; Taylor, J. W.*; Llobet, A.*; Trouw, F.*; Kakurai, Kazuhisa; et al.

Journal of the Physical Society of Japan, 79(3), p.034707_1 - 034707_4, 2010/03

 Times Cited Count:16 Percentile:66.37(Physics, Multidisciplinary)

Journal Articles

Magnetic structure of CoO studied by neutron and synchrotron X-ray diffraction

Tomiyasu, Keisuke*; Inami, Toshiya; Ikeda, Naoshi*

Physical Review B, 70(11), p.184411_1 - 184411_6, 2004/11

 Times Cited Count:43 Percentile:83.24(Materials Science, Multidisciplinary)

Below $$T$$$$_{N}$$ = 289 K, the antiferromagnet CoO exhibits magnetic long-range order described by a propagation vector along the trigonal axis, whereas the lattice is distorted monoclinicly along both the tetragonal and the trigonal axes. In order to elucidate this inconsistency, we performed neutron and synchrotron X-ray diffraction experiments on single crystals of CoO, and found a new series of magnetic reflections represented by a propagation vector along the tetragonal axis below $$T$$$$_{N}$$N. These results suggest an altered magnetic structure of CoO, which includes both the trigonal and the tetragonal propagation vectors, has a monoclinic symmetry and which is in accordance with the distorted lattice symmetry.

Oral presentation

Powder inelastic neutron scattering study of infinite-layer ferrite SrFeO$$_{2}$$

Tomiyasu, Keisuke*; Kageyama, Hiroshi*; Tsujimoto, Yoshihiro*; Yoshimura, Kazuyoshi*; Taylor, J. W.*; Llobet, A.*; Kakurai, Kazuhisa; Yamada, Kazuyoshi*

no journal, , 

no abstracts in English

Oral presentation

Polarised neutron spectrometer, POLANO, at J-PARC attempts at understanding novel magnetism

Oyama, Kenji*; Yokoo, Tetsuya*; Ito, Shinichi*; Suzuki, Junichi*; Iwasa, Kazuaki*; Sato, Taku*; Kira, Hiroshi*; Sakaguchi, Yoshifumi*; Ino, Takashi*; Oku, Takayuki; et al.

no journal, , 

Oral presentation

Magnetic diffuse scattering in the triangular-lattice antiferromagnet CuCrO$$_2$$

Kajimoto, Ryoichi; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Okuda, Tetsuji*; Tomiyasu, Keisuke*

no journal, , 

no abstracts in English

Oral presentation

Low-energy spin fluctuations in the triangular-lattice antiferromagnet CuCrO$$_2$$

Kajimoto, Ryoichi; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Tomiyasu, Keisuke*; Okuda, Tetsuji*

no journal, , 

no abstracts in English

Oral presentation

Magnetic properties of quantum spin system Rb$$_2$$Cu$$_2$$Mo$$_3$$O$$_{12}$$ studied by $$mu$$SR technique

Kawamura, Seiko; Tomiyasu, Keisuke*; Koda, Akihiro*; Sari P., D.*; Asih, R.*; Yoon, S. W.*; Watanabe, Isao*; Nakajima, Kenji

no journal, , 

Rb$$_2$$Cu$$_2$$Mo$$_3$$O$$_{12}$$ is a quantum spin system having zig-zag chains of the spin-1/2 Cu ions. Whereas the system is expected to exhibit an incommensurate spin-singlet state based on a ratio of the second neighbor ferromagnetic interaction $$J_2$$ to the first neighbor antiferromagnetic interaction $$J_1$$, there is no report to bare a direct evidence for the spin-singlet ground state of this system. We carried out $$mu$$SR measurements on this system, to clarify its ground state and dynamics. In the zero-field measurement, the time spectra do not show changes with temperature from 300 K to 20 K, while the muon spin relaxation is enhanced below 20 K. The relaxation is again independent of temperature below 1.5 K. The result reveals that the ground state of Rb$$_2$$Cu$$_2$$Mo$$_3$$O$$_{12}$$ is nonmagnetic. Furthermore, the longitudinal-field $$mu$$SR measurements indicate characteristic behavior of the internal field and dynamics accompanying formation of the spin singlet.

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