Browsing by Author "Chen, WT"

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    Commensurate to incommensurate magnetic phase transition in the type-II multiferroic YBaCuFeO5
    (Australian Institute of Physics, 2015-02-06) Lai, YC; Chen, WT; Wang, CW; Rule, KC; Chou, FC; Du, CH
    The simultaneous existence of magnetic and ferroelectric ordering is a characteristic of multiferroic materials. The search for new multiferroics is partly motivated by the need for non-volatile random access memories for which the electric polarisation (magnetisation) is controlled by magnetic field (electric field) or vice versa. The use of such materials would be extremely beneficial for the next generation of electronic devices (mobile phones, tablets etc) whereby compact size constraints are important as well as optimising reading/writing speeds and power consumption. YBaCuFeO5 has been classified as a type-II multiferroic due to its complex magnetic interactions and low temperature feroelectricity. Two magnetic phase transitions of antiferromagnetic nature have been found near TN1 = 450 K and TN2 = 170 K. The first represents the ordering of the Fe3+ ions into a commensurate antiferromagnetic state, while the second represents the ordering of the Cu2+ ions giving an overall incommensurate antiferromagnetic ground state. For the first time, using modified traveling solvent floating zone growth method, we have been able to grow a centimeter-sized, high-quality, singlecrystal of YBaCuFeO5. Magnetisation and neutron diffraction results indicate a complex magnetic phase diagram in this material with a strong hysteresis effect and a chiral magnetic ground state.
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    Weak trimerization in the frustrated two-dimensional triangular Heisenberg antiferromagnet LuyY1−yMnO3
    (American Physical Society, 2023-06-02) Yano, S; Wang, CW; Gardner, JS; Chen, WT; Iida, K; Mole, RA; Louca, D
    To understand the 2D triangular Heisenberg antiferromagnetic system, we investigated the magnetic structures and the dynamics of LuyY1-yMnO3 in detail. The substitutions are adjusted to the Mn atomic position close to xMn=13. The neutron powder diffraction data claims that the magnetic structure of LuyY1-yMnO3 is described as a mixture of Γ3 (P63′cm′) and Γ4 (P63′c′m) at the xMn position for y=0.15, 0.30, and 0.45. The ratio of Γ3 and Γ4 depends on temperature and composition and the fraction of Γ3 increases upon cooling, while no clear trimerization was observed at the xMn position. We estimated exchange parameters from the analysis of the low-energy part of the spin waves. The results showed a weak trimerization effect on cooling because the nearest-neighbor exchange interaction is slightly enhanced. The temperature dependence of the spin-wave dispersion around the Γ point shows that the spin gap closes with increasing temperature because the exchange interactions in the nearest Mn-Mn neighbor become smaller. Gapless diffusive magnetic excitation from a Mn triangular lattice has been observed in a wide range in Q and E space of LuyY1-yMnO3. We found that Lu0.3Y0.7MnO3 could be an ideal case to investigate the trimerization, frustrated magnetism, and magnetoelastic coupling often observed in two-dimensional triangular lattice Heisenberg antiferromagnet systems. ©2023 American Physical Society