Intrinsic and extrinsic contributions to magnetodielectric effect in double perovskite La2CoMnO6 nanoparticles

We have studied the magnetic and magnetodielectric (MD) properties of La2CoMnO6 nanoparticles of size similar to 28 nm prepared by sol-gel method. Dielectric behavior showed two relaxations coinciding with the magnetic transitions at 218 and 150 K, respectively. At those relaxation maxima, a large MD effect of 11 and 8% (at 100 kHz) with 5T was observed and the magnitude of MD effect is dependent on frequency. Delta epsilon(MD) proportional to M-2 relation in the paramagnetic to ferromagnetic regime suggests the spin lattice coupling; however, within the ferromagnetic region (200-100 K), we have found Delta epsilon(MD) proportional to M-4 relation which may be due to the complicated spin-pair correlation interactions among next nearest neighbors. Complex impedance analysis showed large frequency dispersion of dielectric permittivity, and strong influence of both bulk and grain boundary impedances with magnetic field clearly suggests that both intrinsic spin-lattice coupling and extrinsic Maxwell-Wagner model combined with magnetoresistance effect contribute to the observed MD property.