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 spi n-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 m odes can be clearly observed. The phonon and spin-wave energy and damp ing are evaluated for the first time beyond the random-phase approxima tion. The temperature dependence of these quantities is discussed and is found to be in good agreement with the experimental data.