Browsing by Author "Yoshizawa, H"

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    Crystal structure and magnetic properties of the breathing kagome ising antiferromagnet Yb3Ni11Ge4.63
    (The Physical Society of Japan, 2020-07-31) Takahashi, M; Nawa, K; Okuyama, D; Nojiri, H; Frontzek, MD; Avdeev, M; Yoshida, M; Ueta, D; Yoshizawa, H; Sato, TJ
    We have investigated magnetic properties of the rare-earth based intermetallic compound Yb3Ni11Ge4.63 (YNG), where Yb3+ ions form a breathing-kagome lattice. Single-site 4f electron wavefunctions of the ground-state doublet are deduced from magnetization and heat capacity measurements. The Weiss temperatures are quite anisotropic as Θa = −0.01(2) K (H ∥ a) and Θc = −0.67(2) K (H ∥ c), indicating Ising-like spin–spin interactions dominating in this compound. Low-temperature neutron diffraction confirms absence of magnetic Bragg peaks down to 0.05 K, whereas enhancement of broad peaks below 0.8 K was observed, a signature of short-range spin correlations. Competing interactions on the breathing-kagome lattice would suppress a magnetic long-range order in YNG. ©2020 The Physical Society of Japan
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    Degenerate ground state in the classical pyrochlore antiferromagnet Na3Mn(CO3)2Cl
    (American Physical Society, 2018-10-18) Nawa, K; Okuyama, D; Avdeev, M; Nojiri, H; Yoshida, M; Ueta, D; Yoshizawa, H; Sato, TJ
    In an ideal classical pyrochlore antiferromagnet without perturbations, an infinite degeneracy in a ground state leads to the absence of magnetic order and a spin-glass transition. Here we present Na3Mn(CO3)2Cl as a new candidate compound where classical spins are coupled antiferromagnetically on the pyrochlore lattice and report its structural and magnetic properties. The temperature dependences of the magnetic susceptibility and heat capacity and the magnetization curve are consistent with those of an S=5/2 pyrochlore lattice antiferromagnet with nearest-neighbor interactions of 2 K. Neither an apparent signature of a spin-glass transition nor magnetic order is detected in magnetization and heat capacity measurements or powder neutron diffraction experiments. On the other hand, antiferromagnetic short-range order of the nearest neighbors is evidenced by the Q dependence of the diffuse scattering which develops around 0.85Å−1. A high degeneracy near the ground state in Na3Mn(CO3)2Cl is supported by the magnetic entropy, estimated as almost 4JK−2mol−1 at 0.5 K. ©2018 American Physical Society
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    Flux line lattice structure in YNi2B2C
    (Physical Society of Japan, 2008-10) Kawano-Furukawa, H; Ohira-Kawamura, S; Tsukagoshi, H; Kobayashi, C; Nagata, T; Sakiyama, N; Yoshizawa, H; Yethiraj, M; Suzuki, J; Takeya, H
    Recently Nakai et at. reported a theoretical H-T phase diagram of flux line lattice (FLL) structure in which successive transitions from a triangular, a square (square(v)), a triangular and another square (square(g)) occur with increasing a magnetic field. Here square(v) and square(g) indicate the FLL structures reflecting anisotropies in the Fermi velocity and the superconducting gap, respectively. In the case of YNi2B2C, square(v) and square(g) should rotate by 45 degrees. The low field transition from triangular to square(v) is observed in RENi2B2C (RE = Er, Tm, Lu, and Y). However, there is no experimental evidence for the appearance of square(g) phase so far. We studied the FLL structure of YNi2B2C in the higher field region by small-angle neutron scattering. Our results show that a large area of the H-T phase diagram is occupied by square(v) phase and there is no evidence for the appearance of square(g) lattice. © 2008, Physical Society of Japan
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    Magnetism of classical pyrochlore antiferromagnet Na3Mn(CO3)2Cl
    (American Physical Society, 2020-03-03) Nawa, K; Okuyama, D; Avdeev, M; Nojiri, H; Yoshida, M; Ueta, D; Yoshizawa, H; Sato, TJ
    Pyrochlore antiferromagnets have attracted interests in terms of unconventional ground states and spin excitations owing to competing interactions. When its magnetism is dominated by classical spins coupled by Heisenberg interactions, a spin liquid state is expected as its ground state because of infinite degeneracy in the ground state (R. Moessner and J. T. Chalker, Phys. Rev. Lett. 80, 2929 (1998); Phys. Rev. B 58, 12049 (1998).). In this research, we report structural and magnetic properties together with low-temperature neutron diffraction patterns on a new pyrochlore antiferromagnet Na3Mn(CO3)2Cl. The structure of Na3Mn(CO3)2Cl is isotypic with that of the Co-analogue Na3Co(CO3)2Cl, which exhibits all-in-all-out magnetic order below 1.5 K (Z. Fu et al., Phys. Rev. B 87, 214406 (2013)). On the other hand, no magnetic Bragg peak indicating a magnetic order was detected down to 0.05 K in Na3Mn(CO3)2Cl. A high degeneracy near the ground state is suggested by a magnetic entropy estimated from heat capacity experiments and enhancement of diffuse scattering from neutron diffraction experiments. © 2021 American Physical Society
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    Neutron 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
    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 Society
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    Temperature and composition phase diagram in the iron-based ladder compounds Ba1−xCsxFe2Se3
    (American Physical Society, 2015-05-28) Hawai, T; Nambu, Y; Ohgushi, K; Du, F; Hirata, Y; Avdeev, M; Uwatoko, Y; Sekine, Y; Fukazawa, H; Ma, J; Chi, S; Ueda, Y; Yoshizawa, H; Sato, TJ
    We investigated the iron-based ladder compounds (Ba,Cs)Fe2Se3. Their parent compounds BaFe2Se3 and CsFe2Se3 have different space groups, formal valences of Fe, and magnetic structures. Electrical resistivity, specific heat, magnetic susceptibility, x-ray diffraction, and powder neutron diffraction measurements were conducted to obtain a temperature and composition phase diagram of this system. Block magnetism observed in BaFe2Se3 is drastically suppressed with Cs doping. In contrast, stripe magnetism observed in CsFe2Se3 is not so fragile against Ba doping. A new type of magnetic structure appears in intermediate compositions, which is similar to stripe magnetism of CsFe2Se3, but interladder spin configuration is different. Intermediate compounds show insulating behavior, nevertheless a finite T-linear contribution in specific heat was obtained at low temperatures. ©2015 American Physical Society