Theory of nonreciprocal optical effects in antiferromagnets: The case ofCr2O3

A microscopic model of nonreciprocal optical effects in antiferromagnets is developed by considering the case of ${\mathrm{Cr}}_2$ ${\mathrm{O}}_3$ where such effects have been observed. These effects are due to a direct coupling between light and the antiferromagnetic order parameter. This coupling is mediated by the spin-orbit interaction and involves an interplay between the breaking of inversion symmetry due to the antiferromagnetic order parameter and the trigonal field contribution to the ligand field at the magnetic ion. We evaluate the matrix elements relevant for the nonreciprocal second harmonic generation and gyrotropic birefringence. © 1996 The American Physical Society.