Magnetoelastic waves and a group-theoretical determination of selection rules for magnon-phonon interactions in antiferromagnetic FeCl2

The symmetry properties of coupled magnetoelastic waves can be exploited to enable selection rules to be determined for the lifting of accidental degeneracy between a phonon and a magnon with the same wavevector, k, the cause of the lifting of the degeneracy being the magnon-phonon interactions. The lifting of these degeneracies can be studied experimentally, principally by using inelastic neutron-scattering techniques. The author studies group theoretically the magnon-phonon interactions in antiferromagnetic FeCl 2 and determine selection rules for magnon-phonon interactives for wavevectors directed along the special lines of symmetry in the Brillouin zone of this material.