Browsing by Author "Venimadhav, A."

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Antisite disorder driven spontaneous exchange bias effect in La2-xSrxCoMnO6 (0 <= x <= 1)
(2016-03-02)
Murthy, J. Krishna
;
Chandrasekhar, K. D.
;
Wu, H. C.
;
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.
Magnetostructural coupling and multiferroic properties in the spin-frustrated system Ni1-xZnxCr2O4
(2016-11-28)
Chandrasekhar, K. Devi
;
Murthy, J. Krishna
;
Lin, J. -Y.
;
Wu, H. C.
;
Tseng, W. J.
The magnetic phase diagram of Ni1-xZnxCr2O4 demonstrates complex magnetic transitions for x = 0.05 with two long-range magnetic- order transitions at T-C1 = 41K and T-C2 = 17 K. A glasslike feature emerges between TC1 and TC2 with the application of a direct current (dc) magnetic field in alternating current (ac) susceptibility measurements. Dielectric measurements show a change from the conventional dielectric to a quantum-paraelectric-like behavior without anomalies near the magnetic ordering temperature in the range 0.05 <= x <= 1. The strong correlation among magnetic, dielectric, and ferroelectric properties near the structural relaxation temperatures 41 and 17 K confirms the emergence of multiferroic behavior in Ni0.95Zn0.05Cr2O4. A significant x-ray magnetic circular dichroism signal at the Ni site and ac susceptibility measurements indicate a spin-canting behavior between TC1 and TC2. The dilute doping of the non-Jahn-Teller Zn ion in the Jahn-Teller Ni site modulate the different magnetic exchange interactions of Ni and Cr, which could invoke spin-canting and multiferroic behaviors.
Metamagnetic behaviour and effect of field cooling on sharp magnetization jumps in multiferroic Y2CoMnO6
(2014-10-01)
Murthy, J. Krishna
;
Chandrasekhar, K. D.
;
Wu, H. C.
;
Yang, H. D.
;
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