Magnon damping by magnon-phonon coupling in manganese perovskites

Inelastic neutron scattering was used to systematically investigate the spin-wave excitations ~magnons! in ferromagnetic manganese perovskites. In spite of the large differences in the Curie temperatures (TC’s! of different manganites, their low-temperature spin waves have very similar dispersions with the zone-boundary magnon softening and broadening that cannot be explained by the canonical double exchange mechanism. From the wave-vector dependence of the magnon lifetime effects and its correlation with the dispersions of the optical-phonon modes, we argue that a strong magnetoelastic ~magnon-phonon! coupling is responsible for the observed low-temperature anomalous spin dynamical behavior of the manganites.