Anharmonic effects in ferromagnetic semiconductors

A Green function technique is used to study the anharmonic spin-phonon and phonon-phonon interaction effects on optical phonon modes and spin-wave excitations in ferromagnetic semiconductors. The cubic spinels have been investigated because the magnetostriction of these compounds is small and the direct contribution of spin ordering to the phonon modes can be clearly observed. The phonon and spin-wave energy and damping are evaluated for the first time beyond the random-phase approximation. The temperature dependence of these quantities is discussed and is found to be in good agreement with the experimental data.