Browsing by Author "Yuan, J. K."

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Anisotropic spin-flip-induced multiferroic behavior in kagome Cu3Bi(SeO3)(2)O2Cl
(2017-03-15)
Wu, H. C.
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Chandrasekhar, K. Devi
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Yuan, J. K.
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Huang, J. R.
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Lin, J. -Y.
Compared to the previous report on Cu3Bi(SeO3)(2)O2X (X = Cl, Br) [V. Gnezdilov et al., (arXiv: 1604.04249)], where no dielectric anomaly was observed without magnetic field near T-N similar to 25.6K, we further present the dielectric behaviors without and with magnetic field in Cu3Bi(SeO3)(2)O2Cl. At zero field H = 0, an antiferromagnetic transition from magnetization and specific heat measurements is clearly established at T-N, while no dielectric anomaly was observed. Those results are similar to the previous report [V. Gnezdilov et al., (arXiv: 1604.04249)]. Above the critical field H-c similar to 0.8 T, a metamagnetic spin-flip transition from antiferromagnetic to ferrimagnetic order at T similar to T-N is induced anisotropically only for H broken vertical bar broken vertical bar c. Meanwhile, a ferroelectric behavior from dielectric and pyroelectric current measurements is observed below T similar to T-N; then a corresponding type-II multiferroics emerges above H-c. The key mechanism of the anisotropic spin-flip-induced multiferroicity in Cu3Bi(SeO3)(2)O2Cl can be ascribed to the breaking of magnetic twofold symmetry in the bc plane above H-c.
Observation of charge-transfer-driven antiferroelectricity in 3d-pyrochlore multiferroic Cu2OCl2
(2019-03-01)
Wu, H. C.
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Yuan, J. K.
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Chandrasekhar, K. D.
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Lee, C. H.
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Li, W. H.
Very recently, multiferroic behavior close to the boiling temperature of liquid nitrogen was reported in oxohalide-based Cu2OCl2. In this study, we have established yet another novel mechanism for the origin of charge ordering in multiferroic Cu2OCl2. The direct current (DC) magnetization, specific heat, and neutron diffraction measurements confirm the antiferromagnetic (AFM) ordering (T-N) of Cu2OCl2 near 70 K. The collinear AFM spin structure in Cu(2)OCl(2)was obtained from neutron powder diffraction experiments based on the fitting to the combination of two irreducible representations-Gamma(1)circle plus Gamma(2). Electrical properties, such as dielectric constant, pyroelectric current, and polarization-electric field hysteresis-loop measurements, together suggest a long-range antiferroelectric ordering near T-E approximate to 75 K. The charge transfer from Cl to O along the c-axis was found to induce antiferroelectricity near TE and is supported from ab initio calculations. This finding largely reduces the possibility of well-known Dzyaloshinskii -Moriya interaction in the observed multiferroic behaviors and provides insight into the various origins of high-T-c multiferroics. (C) 2018 Elsevier Ltd. All rights reserved.