Interatomic exchange in Mn-doped III–V semiconductors

Density-functional calculations are used to determine the electronic structure and magnetic properties of dilute magnetic semiconductors with the composition X 1−x Mn x N ( X =Al, Ga, In, x =6.25% and 12.5%). Emphasis is on the interatomic exchange as a function of the Mn–Mn distance. Our superlattice calculations show that the Mn dopants are spin-polarized with a half-metallic band gap and a magnetic moment of 4 μ B per Mn atom at x =6.25 and 12.5%. The Mn (3 d ) bands lie in the band gap but partially hybridize with valence band or N 2 p electrons, depending on the group-III element and on the spin direction. To calculate the exchange interaction parameters J ij, we have used a Green-function approach. The interaction between Mn atoms extends over several interatomic interactions and is mediated by nitrogen (2 p ) electrons. The exchange is always ferromagnetic and largest for the first nearest neighbors, but substantial ferromagnetic interactions persist over Mn–Mn distances up to sixth nearest neighbors in the considered supercell.