Observation of two-critical-angle phenomenon in spin wave resonances in diluted ferromagnetic semiconductor GaMnAs thin films

Abstract

We have studied surface anisotropy energy and surface pinning parameters of ferromagnetic semiconductor GaMnAs film by analyzing spin wave resonance (SWR) measurements carried out on this material. The SWR spectra were observed in various polar and azimuthal angular orientations of external static magnetic field with respect to crystal axes of an annealed GaMnAs film with a Mn concentration of 8.0 at.%). The observed SWR spectra were interpreted in terms of a recently developed spherical surface pinning (SSP) theory. As predicted by the SSP theory, our data clearly show the existence of two critical angles in specific resonance configurations. The experimental confirmation of this key prediction of the SSP model brings new insights into the behavior of magnetic surface anisotropy of GaMnAs films. In particular, the agreement of our experimental results with SWR theory shows that, by including higher-order terms with cubic symmetry in the description of the surface free energy, our analysis will improve our understandings of the magnetic surface anisotropy of GaMnAs films.