Magnon-phonon effects in ferromagnetic manganites

A model is presented for the magnon-phonon interaction in three-dimensional cubic ferromagnetic systems. The Heisenberg Hamiltonian for localized spins is used. The calculated magnon and phonon dampings are compared with the experiments and good agreement is found. It is estimated that there is a significant broadening in the magnon linewidth at the end of the zone and that the phonon linewidth is not affected by this mechanism. The modified magnon spectrum is also evaluated and compared to experimental measurements. It is found that the model predicts softening of the magnon mode at the end of the zone consistent with the experiments. The contribution from both Mn and O atoms is included. The developed model can be applied to systems with reduced dimensions and systems with different than cubic symmetry.