Magnetoelastic waves in rare-earth intermetallics

A theory of low frequency magnetoelastic waves is developed for rare-earth intermetallic compounds crystallizing in the Laves-phase (C15) structure. The long-wavelength modes of the lattice are calculated in terms of three sets of force constants. The triply-degenerate set of oscillations in which only the rare earths move is shown to be the only set which can couple to the magnetization and external strain. A model Hamiltonian is developed which incorporates the energy of this mode and its interaction with acoustic vibrations and magnetization fluctuations.