Magnon-magnon and magnon-phonon relaxation in FeF2

The relaxation of the k↘=0 magnon in the antiferromagnet FeF2 is studied theoretically. Several magnon‐magnon and magnon‐phonon interaction processes are investigated. It is shown that despite the large magnetoelastic interaction in FeF2, magnon‐phonon processes give negligible contribution the the lindewidth. The existing temperature dependent linewidth measurements can be accounted for by four‐magnon processes.