Model for the Surface Anisotropy Field Observed in Spin-Wave Resonance in (Ga,Mn)As Thin Films

Abstract

Dilute ferromagnetic semiconductors are a class of very promising materials of the future [1 6]. Gallium manganese arsenide (Ga,Mn)As, created on the basis of the semiconductor gallium arsenide by the addition of a small percentage of manganese as a magnetic dopant, is one of the most intensively studied compounds in this class [7 12]. Spin-wave resonance in thin lms has been studied particularly intensively in gallium manganese arsenide in the past decade [13 21]. Especially rich resonance spectra were obtained in studies with a variable con guration of the static eld with respect to the lm surface. The eld was rotated perpendicularly to the lm surface, which corresponds to variable polar angle θH between the direction of the external eld and the surface normal. In the present paper we shall analyze SWR measurement data concerning the out-of-plane rotation of the magnetic eld, mainly because of the controversy that arose in the interpretation of these results over an issue which therefore requires elucidation. If researchers tend to agree on the interpretation of SWR spectra in two extreme con gurations the perpendicular and parallel con gurations, corresponding to θH = 0 and θH = 90 ◦, respectively the interpretation of results obtained in intermediate con gurations is under debate. Almost as a rule, a particular con guration of the external eld tends to occur in this range at a critical angle θ H , for which the multi-peak SWR spectrum collapses to a single-peak FMR spectrum. There are two schools of thought regarding the interpretation of the occurrence of this critical angle. Both schools agree that in the critical con guration the thin lm is magnetically homogeneous, and the boundary conditions (speci cally, the surface spin pinning) correspond to the natural conditions, only resulting from the reduced neighborhood of the surface