Systematic Study of Anisotropic Magnetoresistance in (Ga,Mn)As

We systematically study the anisotropic magnetoresistance (AMR) on a series of optimized (Ga,Mn)As samples. The crystalline and non-crystalline contributions to the AMR were separated and an apparent higher-order term (of six-fold symmetry) was identified to be an artefact resulting from the presence of magnetic anisotropy of the material and of the residual fields of external superconducting magnets. In the broad range of nominal Mn concentrations from 2% to 11%, we find the non-crystalline contribution to dominate, although the crystalline terms become relatively more important for higher doping levels. We compare the AMR magnitude with the Boltzmann transport calculations based on the k·p mean-field kinetic-exchange model.