Beyond Virtual Crystal and Molecular Field Approximations in Diluted Magnetic Semiconductors
J. Tworzydło
Institute of Theoretical Physics, Warsaw University, Hoża 69, 00-681 Warszawa, Poland
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The framework of the virtual crystal approximation and the molecular field approximation has been widely used in the description of the extended states affected by the presence of the p-d exchange interaction in diluted magnetic semiconductors. We review shortly the known examples of diluted magnetic semiconductors systems which are described beyond these approx­imations. The interesting case constitutes the nearly binding impurity po­tential in Cd1-xΜnxS. The lattice approaches developed earlier allowed to prove in this case the breakdown of the virtual crystal approximation for low concentrations of magnetic ions and to explain the apparent concentra­tion dependence of the exchange integral. We take explicitly into account the substitutional disorder neglected in the lattice theories and we rederive these results within the dilute and the average t-matrix alloy approach. We generalize systematically this theory to include also the magnetic disorder of the dilute spin subsystem appearing at finite temperatures. When the off-diagonal exchange scattering terms are taken into account in our calcula­tions, we get a good agreement with the experimental data on the asymmetric field dependent spin splitting and the zero-field concentration dependence of the energy gap.
DOI: 10.12693/APhysPolA.88.655
PACS numbers: 71.55.Gs, 75.50.Ρp