The theory of excitons in anisotropic magnetic crystals

We investigate the field dependence of excitonic states in antiferrodielectrics of low symmetry. We calculate the integral intensities of two-particle transitions in magnetic fields which do not disturb the collinear arrangement of spins in the sublattices. Using a specific energetic structure of the ion Fe2+ in siderite, and the special features of the exchange interactions in this crystal, we discuss the microscopic mechanism of the metamagnetic transition and optical properties of FeCO3.