Role of Correlation and Exchange for Quasi-particle Spectra of Magnetic   and Diluted Magnetic Semiconductors
  Theoretical foundation and application of the generalized spin-fermion (sp-d) exchange lattice model to magnetic and diluted magnetic semiconductors are discussed. The capabilities of the model to describe spin quasi-particle spectra are investigated. The main emphasis is made on the dynamic behavior of two interacting subsystems, the localized spins and spin density of itinerant carriers. A nonperturbative many-body approach, the Irreducible Green Functions (IGF) method, is used to describe the quasi-particle dynamics. Scattering states are investigated and three branches of magnetic excitations are calculated in the regime, characteristic of a magnetic semiconductor. For a simplified version of the model (Kondo lattice model) we study the spectra of quasi-particle excitations with special attention given to diluted magnetic semiconductors. For this, to include the effects of disorder, modified mean fields are determined self-consistently. The role of the Coulomb correlation and exchange is clarified by comparing of both the cases. 
A. L. Kuzemsky