A group theoretical study of selection rules for magnon-phonon interactions in ferromagnetic hcp metals

Abstract

The symmetry properties of magnetoelastic waves are exploited to enable selection rules to be determined for the lifting of accidental degeneracy between a phonon and a magnon with the same value of k, the cause of the lifting of the degeneracy being the magnon-phonon interactions. The results are given in detail for ferromagnetic hcp metals and are compared with the published dispersion relations obtained from inelastic neutron scattering experiments on Gd, Tb and Dy. These results are independent of the mechanism postulated for the magnon-phonon interactions. The relation of these general selection rules to selection rules for particular mechanisms is also discussed.