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- ItemDimensional 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
Show more 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)Show more - ItemGapless 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
Show more 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 LimitedShow more - ItemA layered wide-gap oxyhalide semiconductor with an infinite ZnO2 square planar sheet: Sr2ZnO2Cl2(Royal Society of Chemistry, 2017-03-13) Su, Y; Tsujimoto, Y; Miura, A; Asai, S; Avdeev, M; Ogino, H; Ako, M; Belik, AA; Masuda, T; Uchikoshi, T; Yamaura, K
Show more A new square-planar zinc oxyhalide, Sr2ZnO2Cl2, was successfully synthesized using a high-pressure method. Absorption spectroscopy revealed an indirect band gap of 3.66 eV. Electronic structure calculations indicated a strong hybridization between Zn 3dx2−y2 and O 2p orbitals, which is distinct from tetrahedrally coordinated ZnO. © Royal Society of Chemistry 2021Show more - ItemMagnetic order in frustrated Kagome-Triangular lattice antiferromagnet NaBa2Mn3F11(American Physical Society, 2017-03) Hayashida, S; Ishikawa, H; Okamoto, Y; Okubo, T; Hiroi, Z; Avdeev, M; Manuel, P; Hagihala, M; Soda, M; Masuda, T
Show more We performed powder neutron diffraction experiments on NaBa2Mn3F11 [1], a model compound of \textit{Kagome-Triangular} lattice where three of six next-nearest neighbor interactions are non-negligible. More than 10 magnetic Bragg peaks are clearly observed below T= 2 K, meaning that the ground state is a magnetically ordered state. From indexing the magnetic Bragg peaks, magnetic propagation vector of \textbf{\textit{q}}0= (0, 0, 0) and two incommensurate vectors which are close to (1/3, 1/3, 0) are identified. Combination of representation analysis and Rietveld refinement reveals that the propagation vector of \textbf{\textit{q}}0 exhibits the 120º structure in the \textit{ab}-plane. Our calculation of the ground state suggests that the non-negligible magnetic dipolar interaction is responsible for the determined 120º structure in NaBa2Mn3F11. © 2021 American Physical SocietyShow more - ItemMagnetic order in the chemically substituted frustrated antiferromagnet CsCrF 4(American Physical Society, 2020-11-24) Hayashida, S; Hagihala, M; Avdeev, M; Miura, Y; Manaka, H; Masuda, T
Show more The effect of chemical substitution on the ground state of the geometrically frustrated antiferromagnet CsCrF4 has been investigated through a neutron powder diffraction experiment. Magnetic Fe-substituted CsCr0.94Fe0.06F4 and nonmagnetic Al-substituted CsCr0.98Al0.02F4 samples are measured, and magnetic Bragg peaks are clearly observed in both samples. Magnetic structure analysis revealed a 120∘ structure having a magnetic propagation vector kmag=(0,0,1/2) in CsCr0.94Fe0.06F4. For CsCr0.98Al0.02F4, a quasi- 120∘ structure having kmag=(1/2,0,1/2) is formed. It is notable that the identified magnetic structure in CsCr 0.94Fe0.06F4 belongs to a different phase of ground states from those in CsCr0.98Al0.02F4 and the parent CsCrF4. These results suggest that the Fe substitution strongly influences the ground state of CsCrF4.©2020 American Physical SocietyShow more - ItemMagnetic order in the rare-earth ferroborate CeFe3(BO3)4(American Physical Society, 2018-12-04) Hayashida, S; Asai, S; Kato, D; Hasegawa, S; Avdeev, M; Cao, H; Masuda, T
Show more We have studied the magnetic order of the rare-earth ferroborate CeFe3(BO3)4 through the thermodynamic and the neutron diffraction measurements. The heat capacity and the magnetic susceptibility revealed antiferromagnetic magnetic ordering at 29 K. In the neutron powder diffraction data, we observed the magnetic Bragg peaks indexed by the commensurate (CM) propagation vector kCM=(0,0,32) and the incommensurate (ICM) vector kICM=(0,0,32+δ). The incommensurability δ increases with decreasing the temperature, and is evaluated to be 0.04556(16) at 3.7 K. Magnetic structure analysis reveals that the magnetic moments aligning in the ab plane form the collinear antiferromagnetic structure having kCM and helical structure having kICM. Detailed measurements of the magnetic susceptibility exhibit an additional anomaly at 27 K. Furthermore, the temperature dependence of the neutron diffraction profile on the single-crystal sample shows that the ICM and CM ordering occurs at 29 and 26 K, respectively. These results suggest a phase separation state between the collinear and helical structures. The multiferroicity of CeFe3(BO3)4 is discussed on the basis of the determined magnetic structure. ©2018 American Physical SocietyShow more - ItemMagnetic ordering of the buckled honeycomb lattice antiferromagnet Ba2NiTeO6(American Physical Society, 2016-01-19) Asai, S; Soda, M; Kasatani, K; Ono, T; Avdeev, M; Masuda, T
Show more We investigate the magnetic order of the buckled honeycomb lattice antiferromagnet Ba2NiTeO6 and its related antiferromagnet Ba3NiTa2O9 by neutron diffraction measurements. We observe magnetic Bragg peaks below the transition temperatures, and identify propagation vectors for these oxides. A combination of representation analysis and Rietveld refinement leads to a collinear magnetic order for Ba2NiTeO6 and a 120∘ structure for Ba3NiTa2O9. We find that the spin model of the bilayer triangular lattice is equivalent to that of the two-dimensional buckled honeycomb lattice having magnetic frustration. We discuss the magnetic interactions and single-ion anisotropy of Ni2+ ions for Ba2NiTeO6 in order to clarify the origin of the collinear magnetic structures. Our calculation suggests that the collinear magnetic order of Ba2NiTeO6 is induced by the magnetic frustration and easy-axis anisotropy. ©2016 American Physical SocietyShow more - ItemMagnetic state selected by magnetic dipole interaction in the kagome antiferromagnet NaBa2Mn3F11(American Physical Society, 2018-02-12) Hayashida, S; Ishikawa, H; Okamoto, Y; Okubo, T; Hiroi, Z; Avdeev, M; Manuel, P; Hagihala, M; Soda, M; Masuda, T
Show more We haved studied the ground state of the classical kagome antiferromagnet NaBa2Mn3F11. Strong magnetic Bragg peaks observed for d spacings shorter than 6.0 Å were indexed by the propagation vector of k0=(0,0,0). Additional peaks with weak intensities in the d-spacing range above 8.0 Å were indexed by the incommensurate vector of k1=[0.3209(2),0.3209(2),0] and k2=[0.3338(4),0.3338(4),0]. Magnetic structure analysis unveils a 120∘ structure with the tail-chase geometry having k0 modulated by the incommensurate vector. A classical calculation of the Heisenberg kagome antiferromagnet with antiferromagnetic second-neighbor interaction, for which the ground state a k0120∘ degenerated structure, reveals that the magnetic dipole-dipole (MDD) interaction including up to the fourth neighbor terms selects the tail-chase structure. The observed modulation of the tail-chase structure is attributed to a small perturbation such as the long-range MDD interaction or the interlayer interaction. ©2018 American Physical SocietyShow more - ItemMagnetic states of coupled spin tubes with frustrated geometry in CsCrF 4(Nature Publishing Group, 2019-04-23) Hagihala, M; Hayashida, S; Avdeev, M; Manaka, H; Kikuchi, H; Masuda, T
Show more When a theoretical model is realized in nature, small perturbation terms play important roles in the selection of the ground state in geometrically frustrated magnets. In case of a triangular spin tube, the two-dimensional network of the inter-tube interaction forms characteristic lattices. Among them Kagome-Triangular (KT) lattice is known to exhibit an enriched phase diagram including various types of non-trivial structures: non-coplanar cuboc structure, coplanar 120° structure with the two-dimensional propagation vector of k2D = (0, 0), 3–√×3–√ structure with k2D = (1/3, 1/3), and incommensurate structure. We investigate the magnetic state in the model material CsCrF4 by using neutron diffraction technique. Combination of representation analysis and Rietveld refinement reveals that a very rare structure, i.e., a quasi-120° structure with k2D = (1/2, 0), is realized at the base temperature. The classical calculation of the phase diagram elucidates that CsCrF4 is the first experimental realization of the KT lattice having ferromagnetic Kagome bond. A single-ion anisotropy and Dzyaloshinskii-Moriya interaction play key roles in the selection of the ground state. Furthermore, a successive phase transition having an intermediate state represented by k2D = (1/3, 1/3) is observed. The intermediate state is a partially ordered 120° structure which is induced by thermal fluctuation. © 2019, The Author(s)Show more - ItemMagnetic structure and dielectric state in the multiferroic Ca2CoSi2O7(The Physical Society of Japan, 2017-05-10) Soda, M; Hayashida, S; Yoshida, T; Akaki, M.; Hagiwara, M; Avdeev, M; Zaharko, O; Masuda, T
Show more The magnetic structure of the multiferroic Ca2CoSi2O7 was determined by neutron diffraction techniques. A combination of experiments on polycrystalline and single-crystal samples revealed a collinear antiferromagnetic structure with the easy axis along the 〈100〉 directions. The dielectric state is discussed in the framework of the spin-dependent d–p hybridization mechanism, leading to the realization of the antiferroelectric structure. The origin of the magnetic anisotropy is discussed in comparison with that of the isostructural Ba2CoGe2O7. ©2017 The Physical Society of JapanShow more - ItemNeutron scattering study in breathing pyrochlore antiferromagnet Ba3Yb2Zn5O11(International Conference on Neutron Scattering, 2017-07-12) Masuda, T; Haku, T; Soda, M; Sera, M; Kimura, K; Taylor, J; Itoh, S; Yokoo, T; Matsumoto, Y; Yu, DH; Mole, RA; Takeuchi, T; Nakatsuji, S; Kohno, Y; Sakakibara, T; Chang, LJ
Show more Comprehensive study on breathing pyrochlore antiferromagnet Ba3Yb2Zn5O11 [1] is presented. To identify the energy scheme of crystalline electric field (CEF), we performed inelastic neutron scattering (INS) measurement in high energy range. The observed dispersionless excitations are explained by a CEF Hamiltonian of Kramers ion Yb3+ of which the local symmetry exhibits C3v point group symmetry. The magnetic susceptibility is consistently reproduced by the energy scheme of the CEF excitations. To identify the spin Hamiltonian we performed INS experiment in low energy range and thermodynamic property measurements at low temperatures. The INS spectra are quantitatively explained by spin-1/2 single-tetrahedron model having XXZ anisotropy and Dzyaloshinskii-Moriya interaction. This model has a two-fold degeneracy of the lowest-energy state per tetrahedron and well reproduces the magnetization curveat 0.5 K and heat capacity above 1.5 K. At lower temperatures, however, we observe a broad maximum in the heat capacity around 63 mK, demonstrating that a unique quantum ground state is selected due to extra perturbations with energy scale smaller than the instrumental resolution of INS. Possible mechanisms for the ground state selection are discussed [2].Show more - ItemNeutron scattering study of magnetic structure in triangle spin tube CsCrF4(American Physical Society, 2016-03) Hagihala, M; Avdeev, M; Manaka, H; Masuda, T
Show more Triangle spin tube viewed from tube direction is topologically equivalent to kagomé lattice. The rung (J1) and inter-tube (J2) interactions on triangle spin tube correspond respectively to the next nearest neighbor and the nearest neighbor interactions on kagomé lattice. In the case of J1>0 (Antiferromagnetic) and J1>>|J2|, the ground state is q=0,120∘ structure with J2>0 or Cuboc state that represented multi-q (q=2π(1/2 0) and two symmetric-equivalent vectors) with J2<0 [1]. CsCrF4 is a perfect triangle spin tube material with antiferromagnetic intra-tube and rung interactions [2]. Neutron diffraction measurement revealed magnetic long-range order at T=1.5 K. Contrary to the expectation, the magnetic structure was determined q=2π(1/2 0 1/2), 120∘ structure by Rietveld refinement. We also confirmed that this structure was stabilized by Dzyaloshinskii -Moriya interaction and small anisotropy that obeyed the three-fold symmetry at Cr sites by calculation. © 2021 American Physical SocietyShow more - ItemNeutron scattering study of the quasi-one-dimensional antiferromagnet Ba2CoSi2O7(American Physical Society, 2019-10-07) Soda, M; Hong, T; Avdeev, M; Yoshizawa, H; Masuda, T; Kawano-Furukawa, H
Show more Magnetization and neutron scattering measurements have been carried out on an antiferromagnet Ba2CoSi2O7. The observed magnetic excitation is almost dispersionless, and the neutron intensity is only modulated along the [101] direction. The dispersionless magnetic excitation suggest that the Ba2CoSi2O7 system is a quasi-one-dimensional antiferromagnet. Classical spin-wave theory for a one-dimensional antiferromagnet can explain the dispersionless spin excitation. The magnetic structure determined by the measurement of the neutron powder diffraction is consistent with no observation of the multiferroic property in this system. ©2019 American Physical SocietyShow more - ItemStripy order in buckled honeycomb lattice antiferromagnet Ba2NiTeO6(International Conference on Neutron Scattering, 2017-07-12) Asai, S; Soda, M; Kasatani, K; Ono, T; Avdeev, M; Garlea, VO; Winn, B; Masuda, T
Show more Ba NiTeO is a rare experimental realization of a buckled honeycomb lattice antiferromagnet. The nearest-neighbor and next-nearest-neighbor interactions in the honeycomb lattice are comparative due to the buckled geometry, leading to magnetic frustration. A magnetic transition is observed at 8.6 K in the susceptibility and heat capacity measurements [1]. The frustration parameter /T is 18.6, where is Weiss temperature and is the magnetic transition temperature. In order to investigate the low temperature state we performed neutron scattering experiments. In the diffraction profile magnetic Bragg peaks are observed at < , and the propagation vector is identified as (0, 1/2,1). Combination of the representation analysis and Rietveld refinement reveals that a collinear stripy structure [2] is realized [3]. Our calculation suggests that the stabilization of the stripy structure instead of spiral structure is ascribed to the competition between magnetic frustration and easy-axis type anisotropy. In the inelastic neutron spectrum at 2 K a magnetic excitation with an energy gap of 2 meV is observed. Spin-wave calculation based on two-dimensional frustrated honeycomb lattice antiferromagnet having easy-axis anisotropy reproduces the experimental data. The obtained parameters are consistent with Weiss temperature estimated from the bulk magnetic susceptibility measurement.Show more