  Results are presented for spin-wave dispersions in geometrically frustrated
stacked triangular antiferromagnets with a thin film or semi-infinite geometry
having either zero, easy-plane, or easy-axis anisotropy. Surface effects on the
equilibrium spin configurations and excitation spectrum are investigated for
the case of antiferromagnetically coupled films, serving to extend previous
results on ferromagnetically coupled layers [E. Meloche et al., Phys. Rev. B
74, 094424 (2006)]. An operator equation of motion formalism is applied to
systems which are quasi-one and quasi-two dimensional in character. In contrast
to the case of ferromagnetically coupled films the new results show surface
modes that are well separated in frequency from bulk excitations. Magnetic
excitations in thin films with an even or an odd number of layers show
qualitatively different behavior. These results are relevant for a wide variety
of stacked triangular antiferromagnetics materials.
