Interstitial Mn in (Ga,Mn)As:: Binding energy and exchange coupling -: art. no. 165212

We present ab initio calculations of total energies of Mn atoms in various interstitial positions. The calculations are performed by the full-potential linearized plane-wave method. The minimum energy is found for tetrahedral T(As-4) position, but the energy of the T(Ga-4) site differs by only a few meV. The T(Ga-4) position becomes preferable in the p-type materials. In samples with one substitutional and one interstitial Mn, the Mn atoms tend to form a close pair with antiparallel magnetic moments. We also use the spin splitting of the valence band to estimate the exchange coupling J(pd) for various positions of Mn. The exchange parameter is the same for the substitutional and for the T(As-4) position, and it is somewhat smaller in the case of the T(Ga-4) position.