Abstract:
Two dilute magnetic semiconductors (DMS) based on III-V and II-VI materials differ in many respects. The isovalent substitution of Mn in II-VI materials makes the alloying easy, Mn impurity bears magnetic moments and is electrically neutral. Without extra doping, (II,Mn)VI materials remain intrinsic semiconductors with antiferromagnetic exchange interactions between the local moments. In III-V semiconductors, on the other hand, Mn impurities act as acceptors and produce holes mediating ferromagnetic exchange coupling. The third group of DMS based on I-II-V semiconductors seems promising: it combines isovalent Mn(Zn) substitution and variable carrier density controlled by Li non-stoichiometry. We present a detailed comparison of the representative materials (Ga,Mn)As, (Zn,Mn)Se, and Li(Zn,Mn)As, based on density functional calculations. We find that at a given concentration x of magnetic ions and density of carriers, the materials are very similar. This reflect their similar band structures. In all cases, we observe a transition from antiferromagnetic to ferromagnetic interaction if the concentration of carriers (either holes or electrons) divided by x exceeds some critical value. We explain the origin the unexpected ferromagnetic state of the n-type materials and show that it could be realized in Li(Zn,Mn)As.

In collaboration with: J. Kudrnovsky, F. Maca, and T. Jungwirth.