A La(2)NiMnO(6) polycrystalline sample prepared by the sol-gel method showed monoclinic crystal structure with the P2(1)/n space group and a saturation magnetization of 4.63 μ(B)/f.u. at 5 K. Impedance spectroscopy results in the temperature range of 10 K < T < 300 K have revealed a distinct conduction process at grains and grain boundaries, where the grains followed the variable range hopping mechanism and the grain boundaries obeyed Arrhenius thermal activation. A negative magnetoresistance of 2.5% was observed at the paramagnetic to ferromagnetic transition, and this became temperature independent below the magnetic ordering. A marginal positive magnetodielectric (MD) effect that followed the dielectric relaxation was observed and its magnitude was found to decrease with increase of the frequency. A systematic study on the magnetic field induced dielectric properties, dc transport and dc bias effect on the dielectric permittivity has revealed the extrinsic origin of the MD effect in the bulk sample of La(2)NiMnO(6).

We report magnetization, dielectric and dc transport properties of La(2)NiMnO(6) nanoparticles. Both dc and ac magnetization measurements indicated a metastable magnetic behaviour with random ferromagnetic and antiferromagnetic interactions below 110 K; critical slow-down, memory and rejuvenation properties signify the spin glass nature. The dc resistivity shows a semiconducting nature but the temperature dependent magnetoresistance (MR) shows a peak at the spin glass transition. The colossal dielectric property and its frequency dependence were interpreted using the Maxwell-Wagner (MW) interfacial polarization model. Impedance analysis along with magnetodielectric (MD) and magnetoresistance (MR) indicates that the observed MD originates from the combined effect of MR and MW interfacial polarization.

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 (Sr(2+)) doping in La(2-x)Sr(x)CoMnO6 (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 Co(2+) and Co(3+) 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.

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We present a large magnetodielectric (MD) effect of 65% at 100 kHz with a 5 T field in a B-site ordered La 2 CoMnO 6 (LCMO) polycrystalline sample. Frequency and temperature dependent impedance and dielectric studies under a magnetic field divulge both intrinsic and extrinsic origins for the observed MD effect. The temperature dependent Raman spectroscopy measurement showed spin-lattice coupling that supports the intrinsic origin of the observed large MD response in LCMO. Extrinsic contributions to MD response mainly originate from disorder and interface effects; here, we signify this by hole carrier (Sr) doping at the A-site of the ordered LCMO sample. The comparison study has disclosed that with the disorder, the intrinsic polarization due to asymmetric hopping decreases significantly, and the disorder induced transport dominates in both MD and magnetoresistance behaviour with close resemblance.