The recently reported Rutherford backscattering and particle-induced X-ray emission experiments 1 have revealed that in low-temperature MBE grown Ga1−xMnxAs a significant part of the incorporated Mn atoms occupies tetrahedral interstitial sites in the lattice. Here we study the magnetic properties of these interstitial (MnI) ions. We show that they do not participate in the hole-induced ferromagnetism. Moreover, MnI double donors may form pairs with the nearest substitutional (MnGa) acceptors -our calculations evidence that the spins in such pairs are antiferromagnetically coupled by the superexchange. We also show that for the Mn ion in the other, hexagonal, interstitial position (which seems to be the case in the Ga1−x−yMnxBeyAs samples) the p-d interactions with the holes, responsible for the ferromagnetism, are very much suppressed.

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The antiferromagnetic type of the interaction between the Γ8 -band electrons and the Mn2 + ions in AIIBIV diluted magnetic semiconductors has been explained by invoking the p-d hybridization mechanism. In this paper it is shown that for particular electronic configurations of the magnetic ions in The kinetic exchange is a second-order process involving two such transitions.Despite the fact that in each transition the electron spin is conserved the effective scattering of band electrons on magnetic ions can be spin-dependent, due to two reasons. Firstly, by the Pauli principle, the possibility of the virtual transitions depends on the relative alignment of the ionic and band electron spins (if, for example, all d-orbitals are occupied by spin-up electrons only the spin-down band electron can hop onto the ion). Secondly, depending on the spin of the band