Anomalous behavior in rare-earth and actinide systems.

Many different anomalous behaviours (intermediate valence, heavy fermions, competition between magnetic order and Kondo effect) have been experimentally observed in alloys and compounds containing anomalous rare-earths, Ce, Yb, Eu and also Pr, Sm and Tm, as well as in systems with non-magnetic actinides U, Np and Pu. This paper reviews theoretical models describing several interesting cases : the transitions accompanied by a valence change such as for example in cerium metal and Eu(Pd1-xAux)(2)Si-2 alloys; the "normal" Kondo effect and the heavy fermion behaviour; the "underscreened" Kondo effect which can be applied to actinide compounds; the occurrence of antiferromagnetic, Kondo, Non Fermi Liquid and spin glass phases in cerium or uranium disordered alloys.