Abstract:
We combine first-principles electronic structure calculations of interatomic exchange interactions in the local density approximation with a classical Heisenberg model and Monte Carlo simulations of both the spin-fluctuations and the positional disorder to estimate critical temperatures of diluted magnetic semiconductors. We show that their magnetic properties are dominated by short-ranged exchange interactions that have a strong directional character. Dependence of exchange interactions on compensating defects and on the electron correlations effects will be also discussed. An agreement of the theory that does not use adjustable parameters is obtained only when magnetic atoms are randomly distributed on the lattice. The ordering in diluted magnetic semiconductors is heavily influenced by magnetic percolation and measured critical temperatures are strongly influenced by details in sample preparation.

References: Phys. Rev. B 69 (2004) 115208
Phys. Rev. Lett. 93 (2004) 137202
Europhys. Lett. 69 (2005) 812

In collaboration with L. Bergqvist, G. Bouzerar, V. Drchal, and I. Turek.