Effect of shape anisotropy on the magnetization reversal process of (Ga,Mn)As ferromagnetic semiconductors

We have carried out the planar Hall effect measurement on two different sizes of Hall bar devices fabricated from GaMnAs ferromagnetic films. The detailed information on the magnetic anisotropy properties including the shape anisotropy field were obtained from the angular dependence of planar Hall resistance. The shape anisotropy field per magnetization in the device with 10 mu m channel width was about 39 G. Though the value of shape anisotropy is small, it affects the magnetization reversal processes of the 10 mu m Hall device by showing steplike feature in the angular dependence of switching fields.