First principles study of the ferromagnetism in Ga1-xMnxAs semiconductors

We have performed ab initio calculations within the density-functional theory for Ga1-xMnxAs diluted semiconductors. Total energy results unambiguously show that a quasi-localized hole, with predominant p-like character, surrounds the fully polarized Mn up arrow d(5)-electrons. The calculations indicate that the holes form a relatively dispersionless impurity band, thus rendering effective-mass descriptions of hole states open to challenge. We obtain estimates both for the s = 1/2 hole and S = 5/2 Mn exchange coupling, and for the distance dependence of the effective Mn-Mn exchange interaction. The results demonstrate that the effective Mn-Mn coupling is always ferromagnetic, and thus non-RKKY, and is intermediated by the antiferromagnetic coupling of each Mn spin to the holes.