Electronic structure and exchange constants in magnetic semiconductor digital alloys: chemical and band-gap effects

First-principles simulations have been performed for [001]-ordered Mn/Ge and Mn/GaAs 'digital alloys', focusing on the effects of (i) a larger band-gap and (ii) a different semiconducting host on the electronic structure of the magnetic semiconductors of interest. Our results for the exchange constants in Mn/Ge, evaluated using a frozen-magnon scheme, show that a larger band-gap tends to give a stronger nearest-neighbor ferromagnetic coupling and an overall enhanced in-plane ferromagnetic coupling even for longer-ranged coupling constants. As for the chemical effects on the exchange constants, we show that Mn/GaAs shows a smaller nearest-neighbor ferromagnetic coupling than Mn/Ge, but exchange constants for higher Mn-Mn distance show an overall increased ferromagnetic behavior in Mn/GaAs. As a result, from the magnetic-coupling point of view, the two systems behave on average rather similarly. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.