FERROMAGNETISM WITHIN THE PERIODIC ANDERSON MODEL - A NEW APPROXIMATION SCHEME

We introduce a new approach to the periodic Anderson model (PAM) that allows a detailed investigation of the magnetic properties in the Kond o as well as the intermediate valence regime. Our method is based on a n exact mapping of the PAM onto an effective medium strong-coupling Hu bbard model. For the latter, the so-called spectral density approach ( SDA) is rather well motivated since it is based on exact results in th e strong coupling limit. Besides the T=0 phase diagram, magnetization curves and Curie temperatures are presented and discussed with help of temperature-dependent quasiparticle densities of state. In the interm ediate valence regime, the hybridization gap plays a major role in det ermining the magnetic behaviour. :Furthermore, our results indicate th at ferromagnetism in this parameter regime is not induced by an effect ive spin-spin interaction between the localized levels mediated by con duction electrons as it is the case in the Kondo regime. The magnetic ordering is rather a single-band effect within an effective f-band.