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J. Kudrnovsky, I. Turek, V. Drchal, F. Maca, P. Weinberger, P. Bruno:
"Exchange interactions in III-V and group-IV diluted magnetic semiconductors";
Physical Review B, 69 (2004), 115208-1 - 115208-11.

Effective pair exchange interactions between Mn atoms in III-V and
group-IV diluted magnetic semiconductors are determined from a two-step
first-principles procedure. In the first step, the self-consistent
electronic structure of a system is calculated for a collinear spin
structure at zero temperature with the substitutional disorder treated
within the framework of the coherent-potential approximation. The
effective exchange pair interactions are then obtained in a second step by
mapping the total energies associated with rotations of magnetic moments
onto an effective classical Heisenberg Hamiltonian using the magnetic
force theorem and one-electron Green functions. The formalism is applied
to Ga12xMnxAs alloys with and without As antisites, and to Ge12xMnx alloys
recently studied experimentally. A detailed study of the behavior of pair
exchange interactions as a function of the distance between magnetic atoms
as well as a function of the concentrations of the magnetic atoms and
compensating defects is presented. We have found that due to disorder and
the half-metallic character of the system the pair exchange interactions
are exponentially damped with increasing distance between the Mn atoms.
The exchange interactions between Mn atoms are ferromagnetic for distances
larger than the ones corresponding to the averaged nearest-neighbor Mn-Mn
distance. The pair exchange interactions are also reduced with increasing
concentrations of the Mn atoms and As antisites. As a simple application
of the calculated exchange interactions we present mean-field estimates of
Curie temperatures.

DOI: 10.1103/PhysRevB.69.115208 PACS number~s!: 75.50.Pp, 71.15.Nc,
71.20.Nr, 75.30.Et

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