TEMPERATURE-DEPENDENT BAND-STRUCTURE OF FERROMAGNETIC METALS WITH LOCALIZED MOMENTS

We consider a theoretical model for ferromagnetic metals like Gd, which takes into account the exchange interaction and the hybridization between two electronic subsystems. The first is built up by quasi-localized electrons, which take care for the existence of permanent magnetic moments, and is described by an atomic limit multiband Hubbard-Hamiltonian. The second subsystem consists of relatively broad conduction bands with more or less ''free'' electrons. We investigate the influence of electron correlations on the conduction band states in dependence of temperature T and bandfilling n. A sensitive reaction of the band states on the magnetic ordering of the moment system leads to strong band deformations. The main goal is the determination of a quasiparticle bandstructure, which we derive in analogy to the experiment (PES, IPE) directly from the spectral density. The new aspect is a splitting of the '' bare '' dispersion epsilon(m)(k) into several quasiparticle dispersion curves with strongly T- and n-dependent spectral weights. Even for T > T(c) an '' exchange-caused '' splitting is found. - In this paper we use as input for the ''free'' band energies epsilon(m)(k) a nondegenerate simple cubic-tight binding expression, and in addition seven dispersionless f-levels, in order to stress mainly the influence of many body effects. It is discussed how the model can be coupled to a LDA bandstructure calculation, in order to get quantitative results for the T-dependent electronic structure of the ferromagnetic 4f-metal Gd, the presentation of which is intended in a forthcoming paper.