Theory of surface spin waves in a stacked triangular antiferromagnet with ferromagnetic interlayer coupling

Abstract

A theory is presented for bulk and surface spin waves in a stacked triangular antiferromagnet with ferromagnetic interlayer coupling. The method exploits triangular symmetry of the system through properties of block-tridiagonal matrices. A theory is developed for spin-wave dispersion relations of a semi-infinite frustrated system as well as for thin films. The influence of surface exchange and anisotropy parameters on surface and bulk spin-wave energies is discussed. The method is applied to obtain numerical results for $\mathrm{Rb}\mathrm{Fe}{\mathrm{Cl}}_{3}$ and $\mathrm{Cs}\mathrm{Cu}{\mathrm{Cl}}_{3}$.