On the existence conditions of surface spin wave modes in (Ga,Mn)As thin films

TL;DR

This paper investigates the conditions under which surface spin wave modes occur in (Ga,Mn)As thin films, revealing that cubic surface anisotropy and the orientation of magnetization relative to crystal axes are key factors.

Contribution

It demonstrates that cubic surface anisotropy determines the existence of surface spin-wave modes, especially around the hard axes of cubic magnetic anisotropy in (Ga,Mn)As films.

Findings

Surface spin-wave modes occur near the hard axes of cubic anisotropy.

Cubic surface anisotropy influences the surface spin pinning conditions.

Hard cubic axes can act as easy axes for surface spin pinning.

Abstract

Spin-wave resonance (SWR) is a newly emerged method for studying surface magnetic anisotropy and surface spin-wave modes (SSWMs) in (Ga,Mn)As thin films. The existence of SSWMs in (Ga,Mn)As thin films has recently been reported in the literature; SSWMs have been observed in the in-plane configuration (with variable azimuth angle $\phi_M$ between the in-plane magnetization of the film and the surface [100] crystal axis), in the azimuth angle range between two in-plane critical angles $\phi_{c1}$ and $\phi_{c2}$. We show here that cubic surface anisotropy is an essential factor determining the existence conditions of the above-mentioned SSWMs: conditions favorable for the occurrence of surface spin-wave modes in a (Ga,Mn)As thin film in the in-plane configuration are fulfilled for those azimuth orientations of the magnetization of the sample that lie around the hard axes of cubic magnetic anisotropy. This implies that a hard cubic anisotropy axis can be regarded in (Ga,Mn)As thin films as an easy axis for surface spin pinning.