Exchange Interactions and Magnetic Percolation in Diluted Magnetic Semiconductors

Abstract

We propose a theory that combines first-principles evaluations of inter-atomic exchange interactions with a classical Heisenberg model and Monte Carlo simulations. Exchange interactions are determined using the magnetic force theorem and the one-electron Green functions. The magnetic properties of diluted magnetic semiconductors are dominated by short ranged interatomic exchange interactions that; have a strong directional dependence. We show that; critical temperatures of a broad range of diluted magnetic semiconductors, involving Mn-doped GaAs and GaN as well as Cr-doped ZnTe, arc reproduced with a good accuracy only when the magnetic atoms arc randomly positioned on the Ga (Zn) sites, whereas in ordered structure of the magnetic atoms results in critical temperatures that are too high. This suggests that the ordering of diluted magnetic semiconductors is heavily influenced by magnetic percolation, and that the measured critical ternperatures should be very sensitive to the details of the sample preparation, in agreement with observations.