Inter-impurity and impurity-host magnetic correlations in semiconductors   with low-density transition-metal impurities
  Experiments on (Ga,Mn)As in the low-doping insulating phase have shown evidence for the presence of an impurity band at 110 meV above the valence band. The motivation of this paper is to investigate the role of the impurity band in determining the magnetic correlations in the low-doping regime of the dilute magnetic semiconductors. For this purpose, we present results on the Haldane-Anderson model of transition-metal impurities in a semiconductor host, which were obtained by using the Hirsch-Fye Quantum Monte Carlo (QMC) algorithm. In particular, we present results on the impurity-impurity and impurity-host magnetic correlations in two and three-dimensional semiconductors with quadratic band dispersions. In addition, we use the tight-binding approximation with experimentally-determined parameters to obtain the host band structure and the impurity-host hybridization for Mn impurities in GaAs. When the chemical potential is located between the top of the valence band and the impurity bound state (IBS), the impurities exhibit ferromagnetic (FM) correlations with the longest range. We show that these FM correlations are generated by the antiferromagnetic coupling of the host electronic spins to the impurity magnetic moment. Finally, we obtain an IBS energy of 100 meV, which is consistent with the experimental value of 110 meV, by combining the QMC technique with the tight-binding approach for a Mn impurity in GaAs. 
Yoshihiro Tomoda, Nejat Bulut, and Sadamichi Maekawa