Surface spin dynamics of antiferromagnetically coupled frustrated triangular films

TL;DR

This paper investigates surface spin-wave dynamics in antiferromagnetically coupled triangular films, revealing distinct surface modes and excitation behaviors influenced by anisotropy and layer parity, extending understanding beyond ferromagnetic systems.

Contribution

It introduces a formalism for analyzing surface spin dynamics in antiferromagnetic triangular films, highlighting differences from ferromagnetic cases and effects of anisotropy and layer number.

Findings

Surface modes are well separated from bulk excitations.

Magnetic excitations differ between films with even and odd layers.

Surface effects significantly influence spin-wave spectra.

Abstract

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.