Magnetic and antiferromagnetic nonreciprocity of light propagation in magnetoelectric CuB2O4

Abstract

The nonreciprocal propagation, reflection, and absorption of light are most strongly pronounced in the magneto-optical Faraday and Kerr effects that are observed in any paramagnetic and diamagnetic material in the presence of a magnetic field, as well as spontaneous nonreciprocal effects in ferromagnets and ferrimagnets. But nonreciprocity in antiferromagnets is not at all an obvious effect. In this paper, we analyze reciprocal and nonreciprocal propagation of light in a magnetoelectric antiferromagnet ${\mathrm{CuB}}_{2}{\mathrm{O}}_{4}$ that demonstrates a large variety of intriguing optical effects. We present a description of the magnetic and antiferromagnetic nonreciprocal propagation and absorption of light on the basis of space and time symmetry considerations in the paramagnetic and commensurate antiferromagnetic state below the N\'eel temperature. We employ the expansion of the dielectric permittivity tensor as a function of the wave vector of propagating light, an applied magnetic field, and the antiferromagnetic and ferromagnetic order parameters. All these contributions to the dielectric permittivity serve as a basis for solving the relevant Maxwell's equations. Such an approach allowed us to establish the basic mechanisms affecting the propagation of light and sources of nonreciprocity, and it can be applied to other antiferromagnetic crystals. Results of calculations are compared with available experimental data for ${\mathrm{CuB}}_{2}{\mathrm{O}}_{4}$.