Investigation of the magnetic anisotropy in ferromagnetic GaMnAs films by using the planar hall effect

The magnetic anisotropy properties of GaMnAs ferromagnetic films have been investigated by using planar Hall effect measurements. The field scan of the planar Hall resistance (PHR) showed a two-step switching behavior indicating a strong cubic anisotropy along the 〈100〉 directions. The difference in the behaviors of the PHR for two applied field directions, [110] and [110], was understood via the well-known uniaxial anisotropy along the [110] direction. In addition to such known effects, we also found the presence of an asymmetry for the [010] and the [100] directions. This new asymmetry phenomenon was explained by introducing an additional uniaxial anisotropy field H _u2 along the [100] and the [100] directions, which coincide with the two directions of cubic anisotropy. The values of the anisotropy fields, cubic (H _c), first uniaxial (H _u1), and second uniaxial (H _u2), were obtained by analyzing the angle dependence of the PHR. Although the value of H _u2 is small, its effect is clearly observed at high temperatures above 25 K, where the transition of the magnetization occurred before the field direction had been reversed during the magnetization reversal process.