Origin of Bulk Uniaxial Anisotropy in Zinc-Blende Dilute Magnetic Semiconductors

It is demonstrated that the nearest-neighbor Mn pair on the GaAs (001) surface has a lower energy for the [(1) over bar 10] direction compared to the [110] case. According to the group theory and Luttinger's method of invariants, this specific Mn distribution results in bulk uniaxial in-plane and out-of-plane anisotropies. The sign and magnitude of the corresponding anisotropy energies determined by a perturbation method and ab initio computations are consistent with experimental results.