Magnetoelectric effect in simple collinear antiferromagnetic spinels

Abstract

We report the discovery of the linear magnetoelectric effect in a family of spinel oxides, $\mathrm{C}{\mathrm{o}}_{3}{\mathrm{O}}_{4}$ and $\mathrm{Mn}{B}_{2}{\mathrm{O}}_{4}$ $(B=\mathrm{Al},\text{Ga})$ with simple collinear antiferromagnetic spin structure. An external magnetic field induces a dielectric anomaly at ${T}_{\mathrm{N}}$, accompanied by the generation of electric polarization that varies linearly with magnetic field. Magnetization and magnetoelectric measurements on a single crystal of $\mathrm{MnG}{\mathrm{a}}_{2}{\mathrm{O}}_{4}$ together with a phenomenological theory suggest that the easy axis direction is [111] with the corresponding magnetic symmetry $\phantom{\rule{4pt}{0ex}}R{\overline{3}}^{\ensuremath{'}}{m}^{\ensuremath{'}}$. The proposed theoretical model of single-ion contribution of magnetic ions located in a noncentrosymmetric crystal environment stands for a generic mechanism for observing magnetoelectric effects in these and other similar materials.