  In order to account for competition and interplay of localized and itinerant
magnetic behaviour in correlated many body systems with complex spectra the
various types of spin-fermion models have been considered in the context of the
Irreducible Green's Functions (IGF) approach. Examples are generalized d-f
model and Kondo-Heisenberg model. The calculations of the quasiparticle
excitation spectra with damping for these models has been performed in the
framework of the equation- of-motion method for two-time temperature Green's
Functions within a non-perturbative approach. A unified scheme for the
construction of Generalized Mean Fields (elastic scattering corrections) and
self-energy (inelastic scattering) in terms of the Dyson equation has been
generalized in order to include the presence of the two interacting subsystems
of localized spins and itinerant electrons. A general procedure is given to
obtain the quasiparticle damping in a self-consistent way. This approach gives
the complete and compact description of quasiparticles and show the flexibility
and richness of the generalized spin-fermion model concept.
