Volume dependence of the Curie temperatures in diluted magnetic semiconductors

Using electronic structure methods and statistical methods, we have studied theoretically the volume dependence of the exchange interactions and Curie temperatures in the diluted magnetic semiconductors. In both Mn-doped GaAs and Mn-doped InAs, the calculated Curie temperatures from numerical exact Monte Carlo simulations are more or less constant for a large volume interval. We have compared the exchange mechanisms in Mn-doped GaAs using both the local density approximation (LDA) and the LDA+U method. It is demonstrated that the magnetic properties are understood within Zener's p-d exchange model for the LDA+U, while in LDA they reflect a mixture between double and p-d exchange mechanisms.