The effects of magnon-magnon interaction on the two-magnon spectra of antiferromagnets

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Abstract
Recent optical experiments have shown that the two-magnon spectra of antiferromagnets cannot be properly understood using simple non-interacting 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 RbMnF3 and to CoF2 where the orbital contribution to the magnetic moment is important. The predicted optical properties are in good agreement with experiment.