Mn-doped ScN: A dilute ferromagnetic semiconductor with local exchange coupling

We present local spin density functional calculations for Mn-doped ScN using the linear muffin-tin orbital method in a supercell approach, including structural relaxation. Mn is found to induce a localized state in middle of the band gap of ScN with t(2g) character which spin splits and leads to a net magnetic moment of about 2-3 mu(B) per Mn. The defect is a deep acceptor with 0/- transition state at about 0.5 eV above the Fermi level. The magnetic moment increases when in the negative charge state by acquiring more e(g) majority spin electrons and will thus persist even in the presence of the commonly found unintentional background n-type doping of ScN. Up to fourth nearest neighbors exchange interactions are found to be ferromagnetic. The experimentally observed high solubility of Mn in ScN, presumably related to their common crystal structure, is favorable for this dilute magnetic semiconductor. Within mean field theory the Curie temperature is estimated to be above 400 K for 3% Mn. While this may be overly optimistic because of the neglect of disorder, the n-type character of ScN adds further interest to this unusual magnetic semiconductor because the spin-split conduction bands are nondegenerate and thus essentially free from spin-orbit coupling induced spin relaxation.