Magnetization reversal and inverse exchange bias phenomenon in the ferrimagnetic polycrystalline compound Er2CoMnO6

Abstract

${\mathrm{Er}}_{2}{\mathrm{CoMnO}}_{6}$ is a ferrimagnetic oxide consisting of both $4f$ and $3d$ magnetic ions in a monoclinic double perovskite crystal structure (space group $P{2}_{1}/n$). The present work probes some novel magnetic features associated with its ferrimagnetic state on a polycrystalline sample of ${\mathrm{Er}}_{2}{\mathrm{CoMnO}}_{6}$. A clear low temperature compensation point followed by negative magnetization is observed in the field-cooled state of the sample. The sample shows a large field-induced change in entropy at very low temperature, which is related to the observed metamagnetism. Interestingly, ${\mathrm{Er}}_{2}{\mathrm{CoMnO}}_{6}$ is found to show remarkable feature of inverse hysteresis loop which is quite rare among bulk ferrimagnets. Presence of three different magnetic ions, with $4f$ moment of Er having larger uniaxial anisotropy, is likely to be responsible for the observed magnetization reversal and inverse hysteresis loop. The sample also shows inverse exchange bias effect, which is presumably related to the negative exchange interaction at the interface of ordered and antisite disordered ferrimagnetic phases. Such antisite disorder is quite common among the metal oxides having double perovskite structure.