Anisotropic magnetoresistance in Ga1-xMnxAs -: art. no. 212407

We have measured the magnetoresistance in a series of Ga1-xMnxAs samples with 0.033less than or equal toxless than or equal to0.053 for three mutually orthogonal orientations of the applied magnetic field. The spontaneous resistivity anisotropy (SRA) in these materials is negative (i.e., the sample resistance is higher when its magnetization is perpendicular to the measuring current than when the two are parallel) and has a magnitude on the order of 5% at temperatures near 10 K and below. This stands in contrast to the results for most conventional magnetic materials where the SRA is considerably smaller in magnitude for those few cases in which a negative sign is observed. The magnitude of the SRA drops from its maximum at low temperatures to zero at T-C in a manner that is consistent with mean-field theory. These results should provide a significant test for emerging theories of transport in this new class of materials.