Magnetization reorientation in Ga_x Mn_1-x As films: Planar Hall effect measurements

The process of magnetization reorientation in a ferromagnetic semiconductor GaMnAs films was investigated using planar Hall effect measurements. In addition to the well-known two-step switching behavior that occurs during this process, we have observed two additional distinct features in field scan data of the planar Hall resistance (PHR). First, the region of the external field required to begin and complete the reorientation of magnetization from one easy axis to another strongly depends on the direction of the applied field. And second, the maximum amplitude of PHR is significantly reduced during magnetization reversal when the applied field is oriented near one of the easy axes of the GaMnAs film. We provide an explanation of these phenomena using the magnetic field dependence of the free-energy density and assuming the coexistence of multiple domains with three different directions of magnetization in the sample.