論文 - 椎名　亮輔

Mechanism of Non-Coplanar Magnetic Ordering Assisted by the Jahn-Teller Effect in UO2

R. Shiina

Journal of the Physical Society of Japan   91   023704-1 - 023704-5   2022年01月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Heavy Fermion Emerging from the Singular Fermi Liquid in Underscreened Kondo Model for Eu Compounds

S Kuniyoshi, R Shiina

Journal of the Physical Society of Japan   90   123702-1 - 123702-4.   2021年11月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Effect of Magnetic Field on Quantum Phase Transition and Heavy Fermion State in a Two-Orbital Impurity Anderson Model

Ryousuke Shiina, Shingo Kuniyoshi

J. Phys. Soc. Jpn.   90   074708-1 - 074708-6   2021年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Valence Fluctuation, Spin-Orbit Coupling, and Magnetic-Nonmagnetic Crossover in Eu Compounds

Shingo Kuniyoshi, Ryousuke Shiina

J. Phys. Soc. Jpn   89   124711-1 - 124711-9.   2020年11月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Theory of Magnetic Ordering and Valence Fluctuation in Nearly Trivalent Eu Compounds

Ryousuke Shiina

J. Phys. Soc. Jpn.   88   113705   2019年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Theory of Field-Insensitive Heavy Fermion in Sm compounds,

椎名 亮輔

AIP Advances   8   101301   2018年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Stability of Spin-Charge Composite Order Phase in an Extended Kondo Lattice Model with General Band Filling

椎名 亮輔

J. Phys. Soc. Jpn.   87   084704   2018年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Properties of heavy fermion in an impurity anderson model with f2 local singlet ground state

Ryousuke Shiina

Journal of the Physical Society of Japan ( Physical Society of Japan )  87 ( 1 ) 014702   2018年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

The Fermi-liquid properties of a two-orbital impurity Anderson model with an f 2 local singlet ground state is studied by the numerical renormalization group method. It is shown that a heavy-fermion (HF) state with a vanishingly small Wilson ratio is realized in the vicinity of the quantum critical point (QCP) between the local-singlet and Kondo-singlet phases. The parameter area in which the HF behavior appears is remarkably enlarged with increasing the excitation energy from the local singlet to triplet states. It is also clarified that the HF state takes place with an intermediate average occupancy of f electrons, reflecting the existence of the QCP under strong valence fluctuation. The possible application of these theoretical results to an unconventional HF state in Sm compounds is discussed.

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Studies on Valence Fluctuation and Orbital Occupancy in an Impurity Anderson Model with f2 Local-Singlet Ground State

R. Shiina

Journal of the Physical Society of Japan   86   034705   2017年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Theory of magneto-transport in spin-charge composite order phase of Sm skutterudite

Shiina R.

Journal of the Physical Society of Japan ( Journal of the Physical Society of Japan )  85 ( 12 )   2016年12月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Continuous control of local magnetic moment by applied electric field in multiferroics Ba2CoGe2O7

Soda M.

Physical Review B ( Physical Review B )  94 ( 9 )   2016年09月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Acoustic Emission Measurements on Metal-Hydrogenation Process by Using Electrochemical Charging Cell

Jiaxiang Piao, Hiroya Shoji, Takahiro Murakami, Ryousuke Shiina, Shuji Harada

MATERIALS TRANSACTIONS ( JAPAN INST METALS )  56 ( 9 ) 1496 - 1500   2015年09月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

In a recent work, a hydrogenation process of palladium has been studied by the acoustic emission (AE) method with a new gas pressure cell. The high H-2 gas pressure condition can, however, be easily provided by an electrochemical hydrogen charging technique. In this paper, characteristic AE power spectra caused by cavitation and/or bubble burst have been appraised by using an electrochemical separated AE cell. A typical AE signal induced by Pd hydride formation has been observed. The fundamental AE mode was 250 kHz in the Pd hydride formation stage, which was equal to the frequency measured by using the gas pressure cell as a standard hydrogenation technique.

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Effect of Magnetic Field on Spin Excitations in the Kondo Lattice Antiferromagnet

Ryousuke Shiina

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN ( PHYSICAL SOC JAPAN )  83 ( 12 ) 124705   2014年12月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

The properties of spin excitations in the antiferromagnetic ordered phase of the Kondo lattice model in a magnetic field are investigated by the S-1 expansion method with S being the magnitude of localized spins. It is shown that the field dependence of magnon dispersion is different from that in the Heisenberg antiferromagnet, showing an enhancement of excitation energy in the entire Brillouin zone. As a result, the magnon states are found to be unstable and to decay into particle-hole excitations in a high magnetic field.

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Coexistence and Competition of Magnetic and Charge Orders in an Extended Kondo Lattice Model for Sm Skutterudite

Ryousuke Shiina

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN ( PHYSICAL SOC JAPAN )  83 ( 9 ) 094706   2014年09月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

The properties of possible ordered phases in Sm skutterudite are studied in the framework of an effective Kondo lattice model derived from the p-f hybridization. In particular, the stable region of coexisting magnetic and charge orders is investigated in detail by changing the strength of crystal and magnetic fields in an Sm J = 5/2 multiplet. It is demonstrated that the coexisting phase does take place when the crystal field splitting is small, whereas it does not for an isolated Gamma(7) or Gamma(8) crystal field ground state. Although the phase usually appears under a finite magnetic field, the mean field theory predicts its existence at zero field in a case of the Gamma(8) ground state. The relationship of these theoretical results with experimental results of SmRu4P12 is discussed.

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Spin-Nematic Interaction in the Multiferroic Compound Ba2CoGe2O7

M. Soda, M. Matsumoto, M. Mansson, S. Ohira-Kawamura, K. Nakajima, R. Shiina, T. Masuda

PHYSICAL REVIEW LETTERS ( AMER PHYSICAL SOC )  112 ( 12 ) 127205   2014年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

We demonstrate the existence of the spin-nematic interactions in an easy-plane type antiferromagnet Ba2CoGe2O7 by exploring the magnetic anisotropy and spin dynamics. The combination of neutron scattering and magnetic susceptibility measurements reveals that the origin of the in-plane anisotropy is an antiferro-type interaction of the spin-nematic operator. The relation between the nematic operator and the electric polarization in the ligand symmetry of this compound is presented. The introduction of the spin-nematic interaction is useful to understand the physics of spin and electric dipole in multiferroic compounds.

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Order Having Disorder in a New Samarium Compound

椎名 亮輔

J. Phys. Soc. Jpn. Online-News and Comments     2014年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

p-f Mixing, Competing Interactions, and Unconventional Magnetism in SmRu4P12,

椎名 亮輔

JPS Conf. Proc.   3   011006   2014年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Theory of Metal-Insulator Transition and Unconventional Magnetic Ordering in SmRu4P12

Ryousuke Shiina

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN ( PHYSICAL SOC JAPAN )  82 ( 8 ) 083713   2013年08月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

Effects of a magnetic field on metal-insulator transition and antiferromagnetic ordering in the skutterudite SmRu4P12 are studied theoretically. It is argued that the p-f hybridization specific to skutterudites is responsible for the transition. An interplay between magnetic and charge interactions derived from the hybridization is shown to be the key to resolving the origin of puzzling thermodynamic and transport properties in a magnetic field.

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Stability of Charge and Magnetic Orderings Due to Competing Interactions in PrFe4P12

Ryousuke Shiina

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN ( PHYSICAL SOC JAPAN )  81 ( 10 ) 105001   2012年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Multipolar Interaction Derived from d-f Hybridization in Pr-Based Filled Skutterudite Compounds

Ryousuke Shiina

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN ( PHYSICAL SOC JAPAN )  81 ( 2 ) 024706   2012年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

The conduction bands of the skutterudite compounds are composed of p orbitals of the pnictogen cages and d orbitals of the transition metal ions. In this paper, we address the effect of hybridization between the d bands and localized 4f states in relation with ordering and fluctuation of multipole moments in Pr-based filled skutterudites. First, we study the properties of a non-degenerate d band around the zone center in the framework of a tight-binding band model. Introducing a realistic form of the d-f hybridization, we show that the a(g) band can be hybridized only with the Gamma(8) orbitals of f electrons. Then, we derive d-f multipolar interactions from the hybridization in the localized limit of f electrons in which the basis states are restricted to the singlet-triplet crystal field states. It is found that the quadrupolar interaction of the O-xy-type becomes predominant in the case of the singlet ground state, whereas the triplet ground state apparently favors the magnetic interaction. The relationship with experimental results in the Pr skutterudites, especially in PrOs4Sb12 and PrFe4As12, is discussed in view of the nature of quadrupolar and magnetic interactions. It is shown that the complex non-collinear magnetic structure of Fe ions observed in the latter material is reproduced well by the effective d-f interaction.

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