Second-order magnetoelectric susceptibility in the optical region of the boraciteCo3B7O13I

Abstract

Nonreciprocal linear birefringence induced by a magnetic field is observed in the cubic phase of ${\mathrm{Co}}_{3}{\mathrm{B}}_{7}{\mathrm{O}}_{13}\mathrm{I}$ single crystals. This effect is one of a class of magneto-induced spatial dispersion phenomena allowed in noncentrosymmetric crystals. It shows S-shaped dispersion and anisotropy in the region of electronic transitions between states of ${\mathrm{Co}}^{2+}$ ions. Microscopic mechanisms of the nonreciprocal birefringence are evaluated on the basis of local optical transitions. The anisotropy of the effect originates in the second-order magnetoelectric susceptibility in optical regions. The S shape of dispersion and the temperature dependence of the effect are explained by the paramagnetic nature of the phenomenon, i.e., by the splitting of Kramers doublets of the ground state of the ${\mathrm{Co}}^{2+}$ ion in the magnetic field.