Surface and interface excitations for bilayer Ising-model systems in a transverse field (abstract)

Abstract

We present some calculations for the surface and interface excitations (spin waves) in layered solid structures which may be represented by the Ising model in a transverse magnetic field. In particular, we consider a two-medium system consisting of a ferromagnetic thin film on a semi-infinite substrate of another ferromagnetic material. By generalizing previous results for a single semi-infinite medium,1,2 we show that there may be excitations localized near the surface and interface of the coupled magnetic system, depending on the parameters of the model. We deduce dispersion relations for these surface and interface spin waves, as well as for the quantized (or ‘‘standing’’) bulk spin waves in the thin film, including the effects of relaxational damping of the modes. For nonzero values of the transverse field, the formalism can be applied at temperatures above and below the critical temperatures in the two media. Although our theory provides a description of some real anisotropic magnetic materials when placed in a transverse magnetic field, it is also of wider applicability within a pseudo-spin formalism for certain order–disorder ferroelectrics and Jahn–Teller systems.