Phys. Rev. B 63, 165206
(2001)
First Principle study of the origin and nature of ferromagnetism in (Ga,Mn)As
S. Sanvito, P. Ordejón and N.A. Hill
The properties of diluted Ga1-x MnxAs
are calculated for a wide range of Mn concentrations within the local-spin-density
approximation of density-functional theory. Mulliken population analyses
and orbital-resolved densities of states show that the configuration of
Mn in GaAs is compatible with either 3 d5 or 3d6; however,
the occupation is not integer due to the large
p-d hybridization
between the Mn d states and the valence band of GaAs. The spin splitting
of the conduction band of GaAs has a mean-field-like linear variation with
the Mn concentration, and indicates ferromagnetic coupling with the Mn
ions. In contrast, the valence band is antiferromagnetically coupled with
the Mn impurities, and the spin splitting is not linearly dependent on
the Mn concentration. This suggests that the mean-field approximation breaks
down in the case of Mn-doped GaAs, and corrections due to multiple scattering
must be considered. We calculate these corrections within a simple free-electron
model, and find good agreement with our ab initio results if a large
exchange constant (Nß=4.5 eV) is assumed.