Browsing by Author "Okabe, H"

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    Dimensional reduction by geometrical frustration in a cubic antiferromagnet composed of tetrahedral clusters
    (Springer Nature, 2021-07-19) Okuma, R; Kofu, M; Asai, S; Avdeev, M; Koda, A; Okabe, H; Hiraishi, M; Takeshita, S; Kojima, KM; Kadono, R; Masuda, T; Nakajima, K; Hiroi, Z
    Dimensionality is a critical factor in determining the properties of solids and is an apparent built-in character of the crystal structure. However, it can be an emergent and tunable property in geometrically frustrated spin systems. Here, we study the spin dynamics of the tetrahedral cluster antiferromagnet, pharmacosiderite, via muon spin resonance and neutron scattering. We find that the spin correlation exhibits a two-dimensional characteristic despite the isotropic connectivity of tetrahedral clusters made of spin 5/2 Fe3+ ions in the three-dimensional cubic crystal, which we ascribe to two-dimensionalisation by geometrical frustration based on spin wave calculations. Moreover, we suggest that even one-dimensionalisation occurs in the decoupled layers, generating low-energy and one-dimensional excitation modes, causing large spin fluctuation in the classical spin system. Pharmacosiderite facilitates studying the emergence of low-dimensionality and manipulating anisotropic responses arising from the dimensionality using an external magnetic field. © 2021, The Author(s)
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    Gapless spin liquid in a square-kagome lattice antiferromagnet
    (Springer Nature Limited, 2020-06-09) Fujihala, M; Morita, K; Mole, RA; Mitsuda, S; Tohyama, T; Yano, SI; Yu, DH; Sota, S; Kuwai, T; Koda, A; Okabe, H; Lee, H; Itoh, H; Hawai, T; Masuda, T; Sagayama, H; Matsuo, A; Kindo, K; Ohira-Kawamura, S; Nakajima, K
    Observation of a quantum spin liquid (QSL) state is one of the most important goals in condensed-matter physics, as well as the development of new spintronic devices that support next-generation industries. The QSL in two dimensional quantum spin systems is expected to be due to geometrical magnetic frustration, and thus a kagome-based lattice is the most probable playground for QSL. Here, we report the first experimental results of the QSL state on a square-kagome quantum antiferromagnet, KCu6AlBiO4(SO4)5Cl. Comprehensive experimental studies via magnetic susceptibility, magnetisation, heat capacity, muon spin relaxation (μSR), and inelastic neutron scattering (INS) measurements reveal the formation of a gapless QSL at very low temperatures close to the ground state. The QSL behavior cannot be explained fully by a frustrated Heisenberg model with nearest-neighbor exchange interactions, providing a theoretical challenge to unveil the nature of the QSL state. © 2020 Springer Nature Limited