Browsing by Author "Noda, Y"

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    Crystal structure of a non-centrosymmetric system, CuY2Ge2O8
    (International Conference on Neutron Scattering, 2017-07-12) Cho, H; Sim, H; Lee, S; Avdeev, M; Noda, Y; Park, JG
    A non-centrosymmeric material doesn’t have an inversion symmetry, which could lead to the intrinsic electric polarization. When this system consists of magnetic ions, the electric polarization of the system can be modified by a so-called magnetoelectric coupling under magnetic field. This multiferroic property has been widely studied not only for physical interest but also for industrial application. We synthesized both single crystal and polycrystalline samples of new multiferroic systems, Cu(Y,La) Ge and determined the crystal structure at 300 and 450 K using high-resolution powder and single crystal diffraction studies. According to our studies, both samples having magnetic Cu2+ ions has a monoclinic unit cell (space group I 1 1) without inversion symmetry. We also determined the high temperature structure that has a more symmetric orthorhombic unit cell (I m m 2). Using the structural information, we could calculate the theoretical electric polarization at room temperature phase and found that it reaches the electric polarization of 9.88 μC/cm2 along the a-axis.
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    Properties of spin-1/2 triangular-lattice antiferromagnets CuY2Ge2O8 and CuLa2Ge2O8
    (American Physical Society, 2017-04-05) Cho, H; Kratochvílová, M; Sim, H; Choi, KY; Kim, CH; Paulsen, C; Avdeev, M; Peets, DC; Jo, Y; Lee, S; Noda, Y; Lawler, MJ; Park, JG
    We found new two-dimensional (2D) quantum (S=1/2) antiferromagnetic systems: CuRE2Ge2O8 (RE=Y and La). According to our analysis of high-resolution x-ray and neutron diffraction experiments, the Cu network of CuRE2Ge2O8 (RE=Y and La) exhibits a 2D triangular lattice linked via weak bonds along the perpendicular b axis. Our bulk characterizations from 0.08 to 400 K show that they undergo a long-range order at 0.51(1) and 1.09(4) K for the Y and La systems, respectively. Interestingly, they also exhibit field induced phase transitions. For theoretical understanding, we carried out the density functional theory (DFT) band calculations to find that they are typical charge-transfer-type insulators with a gap of Eg≅2eV. Taken together, our observations make CuRE2Ge2O8 (RE=Y and La) additional examples of low-dimensional quantum spin triangular antiferromagnets with the low-temperature magnetic ordering. ©2017 American Physical Society