Browsing by Author "Chandrasekhar, K. D."

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Antisite disorder driven spontaneous exchange bias effect in La2-xSrxCoMnO6 (0 <= x <= 1)
(2016-03-02)
Murthy, J. Krishna
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Chandrasekhar, K. D.
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Wu, H. C.
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Yang, H. D.
;
Lin, J. Y.
Doping at the rare-earth site by divalent alkaline-earth ions in perovskite lattice has witnessed a variety of magnetic and electronic orders with spatially correlated charge, spin and orbital degrees of freedom. Here, we report an antisite disorder driven spontaneous exchange bias effect as a result of hole carrier (Sr2+) doping in La2-xSrxCoMnO6 (0 < x < 1) double perovskites. X-ray diffraction and Raman spectroscopy have evidenced an increase in disorder with the increase of Sr content up to x = 0.5 and thereby a decrease from x = 0.5 to 1. X-ray absorption spectroscopy has revealed that only Co is present in the mixed valence of Co2+ and Co3+ states with Sr doping to compensate the charge neutrality. Magnetotransport is strongly correlated with the increase of antisite disorder. The antisite disorder at the B-site interrupts the long-range ferromagnetic order by introducing various magnetic interactions and instigates reentrant glassy dynamics, phase separation and canted type antiferromagnetic behavior with the decrease of temperature. This leads to a novel magnetic microstructure with unidirectional anisotropy that causes a spontaneous exchange bias effect that can be tuned with the amount of antisite disorder.
Metamagnetic behaviour and effect of field cooling on sharp magnetization jumps in multiferroic Y2CoMnO6
(2014-10-01)
Murthy, J. Krishna
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Chandrasekhar, K. D.
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Wu, H. C.
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Yang, H. D.
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Lin, J. Y.
We present sharp magnetization jumps and field-induced irreversibility in magnetization in multiferroic Y2CoMnO6. The appearance of magnetic relaxation and field sweep rate dependence of magnetization jumps resembles the martensite-like scenario and suggests the coexistence of E*-type antiferromagnetic and ferromagnetic phases at low temperatures. In Y2CoMnO6, the critical field required for the sharp jump can be increased or decreased depending on the magnitude and direction of the cooling field; this is remarkably different from manganites or other metamagnetic materials where the critical field increases irrespective of the direction of the applied field cooling. The cooling field dependence on the sharp magnetization jumps has been described by considering exchange pinning mechanism at the interface, like in the exchange bias model. Copyright (C) EPLA, 2014
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.