In-plane uniaxial anisotropy rotations in (Ga,Mn)As thin films

We show, by superconducting quantum interference device magnetometry, that in (Ga,Mn)As films the in-plane uniaxial magnetic easy axis is consistently associated with particular crystallographic directions and that it can be rotated from the [110] direction to the [110] direction by low-temperature annealing. We show that this behavior is hole-density dependent and does not originate from surface anisotropy. The presence of uniaxial anisotropy as well its dependence on the hole concentration and temperature can be explained in terms of the p-d Zener model of the ferromagnetism assuming a small trigonal distortion.