Disorder and the effective Mn-Mn exchange interaction in GaMnAs diluted magnetic semiconductors
arXiv:cond-mat/0505500 · doi:10.1103/PhysRevB.72.125208
Abstract
We perform a theoretical study, using {\it ab initio} total energy density-functional calculations, of the effects of disorder on the exchange interactions for diluted 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 {\it ab initio} total energy calculations, we obtain the effective $\JMn$, from first () all the way up to sixth () neighbors. Calculated results show a clear dependence in the magnitudes of the $\JMn$ with the Mn concentration . 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.
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