Large antisymmetric magnetoresistance across chemically etched GaMnAs nanoconstrictions

We report the observation of a highly antisymmetric magnetoresistance in GaMnAs specimens with lateral nano-constrictions. The experiments were carried out on samples with an in-plane easy axis of magnetization, in in-plane applied magnetic field. We attribute this behavior to the formation of isolated nano-sized islands at the nano-constrictions, whose magnetization can undergo out-of-plane reorientation during switching. The change in resistance is up to 50%, which cannot be explained by the normal anisotropic magnetoresistance in GaMnAs. We propose tunneling anisotropic magnetoresistance as the most likely mechanism for this effect.