On the Existence Conditions of Surface Spin Wave Modes in (Ga,Mn)As Thin Films

Spin-wave resonance is a newly emerged method for studying surface magnetic anisotropy and surface spinwave modes in (Ga, Mn) As thin films. The existence of surface spin-wave modes in (Ga, Mn) As thin films has recently been reported in the literature; surface spin-wave modes 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 surface spin-wave modes: 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.