Effect of pinning-field distribution on the process of magnetization reversal in Ga_1-xMn_xAs films

The process of magnetization reversal in a Ga_1-xMn_xAs film is investigated by using angle-dependent measurements of the planar Hall effect. When a small field (e.g., below 25 Oe) is used, the planar Hall resistance (PHR) displays four stable values arising from the formation of four different multidomain states during the rotation of the external field direction over 360°. Two of these correspond to the sample being fully magnetized along one of the easy axes. It is shown that there are two intermediate states which form when a fraction of the domains populates one easy direction (say, [100]), and the remaining fraction populates an orthogonal easy axis (with magnetizations, say, along the [010] direction). It is further shown that the relative populations of the magnetic domains corresponding to the two orthogonal easy axes can be controlled by the value of the applied field during the process of magnetization reversal. This phenomenon can be understood by considering the differences in domain-pinning fields and their distributions required for crossing the [110] and the [11̄0] directions in the (001) plane of the Ga_1-xMn_xAs film.