How to calculate reliably Curie temperature in diluted ferromagnetic semiconductors?

Georges Bouzerar

Institut Laue Langevin, Grenoble

We present a novel semi-analytic theory to study ferromagnetism in diluted magnetic semi-conductors. The approach based on Green's functions equation of motion method, treats disorder effects exactly in the effective Heisenberg Hamiltonian, and spin fluctuations within a local self-consistent RPA. The exchange couplings entering the disordered Heisenberg Hamiltonian are taken from {\it ab initio} (TB-LMTO) calculations . The theory gives very good agreement with published data for both as grown samples and optimally annealed samples of MnGa1-xAs. Our calculations predict the critical temperatures for MnxGa1-xN lower than in doped GaAs, despite the stronger nearest-neighbour ferromagnetic coupling. The theory is very general and allow to include the effects of clusters and correlation in the disorder. It is also relatively easy to implement and much faster than Monte carlo simulations.