OPTICAL PROPERTIES OF LAYER ANTIFERROMAGNETS WITH K2NIF4 STRUCTURE

The magnetic structure of K2NiF4, K 2MnF4 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.