f-band ferromagnetism in the periodic Anderson model - a modified alloy analogy

We introduce a new approximation scheme for the periodic Anderson model (PAM). The modified alloy approximation represents an optimum alloy approximation for the strong-coupling limit, which can be solved within the coherent-potential-approximation formalism. Zero-temperature and finite-temperature phase diagrams are presented for the PAM in the intermediate-valence regime. The diversity of magnetic properties accessible by variation of the system parameters can be studied by means of quasiparticle densities of states: the conduction band couples either ferromagnetically or antiferromagnetically to the f levels. A finite hybridization is a necessary precondition for ferromagnetism. However, too strong a hybridization generally suppresses ferromagnetism, but can for certain system parameters also lead to a semi-metallic state with unusual magnetic properties. By comparing with the spectral density approximation, the influence of quasiparticle damping can be examined.