EFFECTS OF MAGNON-MAGNON INTERACTION ON THE TWO- MAGNON SPECTRA OF ANTIFERROMAGNETS

Optical experiments have shown that the two-magnon spectra of antiferromagnets cannot be properly understood using simple noninteracting spin-wave theory. In these experiments two magnons are created close together in real space where they interact strongly to produce large observable effects. They therefore provide an excellent opportunity to study magnon-magnon interactions. A general theory of the two-magnon states using Green function methods is developed and the results applied to the spin-only antiferromagnet RbMnF//3 and to CoF//2 where the orbital contribution to the magnetic moment is important. The predicted optical properties are in good agreement with experiment.