Optical properties of layer antiferromagnets with K₂NiF₄ structure

The magnetic structure of K₂NiF₄, K₂MnF₄ and Rb₂MnF₄ can be approximately regarded as a two-dimensional square lattice, which enables the magnetic Green functions to be expressed in terms of elliptic integrals. Using these, the theory of a magnon sideband on an exciton absorption line is compared with the experimental measurements on Rb₂MnF₄, giving reasonable agreement. A prediction is made for the two-magnon Raman lineshape, and the energies of localized modes associated with impurities calculated.