Theory of Mn-doped II-II-V semiconductors

A recently discovered magnetic semiconductor Ba_1-xK_x(Zn_1-yMn_y)2As₂, with its decoupled spin and charge doping, provides a unique opportunity to elucidate the microscopic origin of the magnetic interaction and ordering in dilute magnetic semiconductors (DMSs). We show that (i) the conventional density functional theory accurately describes this material, and (ii) the magnetic interaction emerges from the competition of the short-range superexchange and a longer-range interaction mediated by the itinerant As holes, coupled to Mn via the Schrieffer-Wolff p-d interaction representing an effective Hund's rule coupling JHeff. The key difference between the classical double exchange and the actual interaction in DMSs is that an effective JHeff, as opposed to the standard Hund's coupling J_H, depends on the Mn d-band position with respect to the Fermi level, and thus allows tuning of the magnetic interactions. The physically transparent description of this material may also be applicable in more complicated DMS systems.