Magnetic and dielectric properties of sol-gel derived nanoparticles of double perovskite Y₂NiMnO₆

Nanoparticles of Y2NiMnO6 having diameters around 20 nm were synthesized by a sol-gel method. X-ray data were analysed by Rietveld method. This showed the crystals to have monoclinic structure. X-ray photoelectron spectroscopy studies showed a ratio of Mn3+/Mn4+ equal to 0.64 to be present in the nanocrystals. A small polaron hopping conduction model was found to satisfactorily explain the electrical resistivity behaviour of the samples. The latter exhibited ferromagnetic (FM) properties with a Curie temperature around 92 K. This behaviour was ascribed to a ferromagnetic superexchange interaction between Mn4+ and Ni2+ ions. Spin glass behaviour was ruled out on the basis of ac magnetic susceptibility data. The nanocrystals exhibited a peak in the dielectric constant at a temperature 535 K indicating a ferroelectric transition. This is consistent with the recent theoretical prediction made on the basis of density functional calculations