Light-matter interaction in antiferromagnets: the exchange-induced   magnetic dipole mechanism
  We propose a novel mechanism for exchange-induced exciton-magnon absorptions via hopping between two antiferromagnetically coupled sites and a simultaneous magnetic dipole transition to an excited orbital state. The obtained selection rules correspond to ones for magnetic dipole transitions and are in agreement with the exciton-magnon transitions observed in the quasi one-dimensional Heisenberg antiferromagnet KCuF3. The calculated magnon density of states in combination with a structure dependent factor identifies the observed optical magnon sideband to originate from transverse magnon modes. 
M. V. Eremin, M. A. Fayzullin, Ch. Kant, A. Loidl, and J. Deisenhofer
cond-mat.str-el