Disorder and the effective Mn-Mn exchange interaction in Ga1-xMnxAs diluted magnetic semiconductors

摘要

We perform a theoretical study, using ab initio total energy density-functional calculations, of the effects of disorder on the Mn-Mn exchange interactions for Ga1-xMnxAs diluted magnetic semiconductors. For a 128 atoms supercell, we consider a variety of configurations with 2, 3, and 4 Mn atoms, which correspond to concentrations of 3.1%, 4.7%, and 6.3%, respectively. In this way, the disorder is intrinsically considered in the calculations. Using a Heisenberg Hamiltonian to map the magnetic excitations, and ab initio total energy calculations, we obtain the effective J(n)(Mn-Mn), from first (n=1) all the way up to sixth (n=6) neighbors. Calculated results show a clear dependence in the magnitudes of the J(n)(Mn-Mn) with the Mn concentration x. Also, configurational disorder and/or clustering effects lead to large dispersions in the Mn-Mn exchange interactions, in the case of fixed Mn concentration. Moreover, theoretical results for the ground-state total energies for several configurations indicate the importance of a proper consideration of disorder in treating temperature and annealing effects.