Complete Analytical Solution for the Zero Bandwidth s—f Model

The s—f model, which describes an interacting system of localized magnetic moments and itinerant conduction electrons (magnetic 4f‐, 5f‐systems), is exactly solved in the zero bandwidth limit without further restrictions. The s—f exchange leads to a splitting of the S ‐“band”; into four quasiparticle sub “bands”, the spectral weights of which are strongly temperature ( T )‐ and carrier concentration ( n )‐dependent. For special parameter constellations certain spectral weights disappear, so that corresponding excitations are forbidden. Besides the spectral weights some relevant correlation functions as the average spin‐dependent occupation number 〈 n σ 〉, the density correlation 〈 n σ n — σ 〉 The “mixed” correlation Δ ↑(↓) = 〈S( ± ) c   ↓(↑) c ↑(↓) ± 〉 ± 〈S 1 n↑(↓)〉, and especially the spin‐polarization P = (〈n↑〉 – 〈n↓〉)/(〈n↑〉 + 〈n↓〉) can be formulated as very simple functions of T, n , and spin value S . It is found a qualitatively quite different behaviour of these functions for ferromagnetic s—f coupling (4f‐systems) and antiferromagnetic s—f coupling (5f‐systems).