Remanent magnetization in CoO antiferromagnetic nanoparticles

Abstract

We report a study on the remanent magnetization ${M}_{r}$ induced by field cooling across the ordering temperature ${T}_{N}$ in antiferromagnetic CoO nanoparticles with different sizes. The nanoparticles are composed by a structurally and magnetically ordered core and a structurally ordered and magnetically disordered shell with a thickness of about 2 nm. The ordered core has cell parameters, moments direction, and modulus similar to those of bulk CoO. ${M}_{r}$ is shown to be proportional to the cooling field ${H}_{cool}$. The low-temperature saturation values of ${M}_{r}$ $[{M}_{r}(0)]$ in the CoO nanoparticles are about two orders of magnitude higher than those found for bulk CoO. ${M}_{r}/{M}_{r}(0)$ of CoO nanoparticles scales with temperature in a single curve, independently on the magnitude of ${H}_{cool}$ and on nanoparticles size, except for temperatures near to ${T}_{N}$ since ${T}_{N}$ is size dependent.