A Green’s-function technique is used to study the influence of spin-phonon interactions in the Ising model with a transverse field (describing KDP-type ferroelectrics) including higher-order anharmonic terms. The renormalized spin-wave and phonon energy, the damping of the spin waves, and the phonon damping have been evaluated. The contribution of the anharmonicity is at low temperatures very small, but at temperatures near the ferroelectric critical temperature ${\mathit{T}}_{\mathit{c}}$, and above ${\mathit{T}}_{\mathit{c}}$, it increases strongly.

• Received 18 April 1994

DOI:https://doi.org/10.1103/PhysRevB.50.5899