INTERMEDIATE VALENCE: THEORETICAL MODELS FOR ANOFALOUS RARE-EARTH ALLOYS AND COMPOUNDS

Rbsum6.- On dgcrit ici les propribtgs magngtiques des systsmes de terres rares anormales. D'abord, on rappelle les rgsultats des modbles b une impuretb qui sont appliques aux alliages ou composgs Kondo et aux systCmes de valence intermgdiaire (cerium, SmS ou alliages Lace). Ensuite, on discute les modsles du "rbseau Kondo" et du "rsseau dlAnderson"qui sont utilisbs pour expliquer le comportement de basse temperature des composbs tels que CeA12, CeAl ou TmSe. 3 Abstract.- The magnetic properties of anomalous rare-earth systems are described here. Pirstly, the main results of the one-impurity models are recalled and applied to Kondo alloys or compounds and to intermediate valence systems (cerium, SmS, &gCe alloys). Then, the "Kondo lattice " or "Anderson lattice " models are discussed and used to explain the low temperature behaviour of compounds such as CeA12, CeA13 or TmSe. 1. Introduction.- The rare-earth metals, alloys and compounds can be divided in two groups: the "normal " rare-earths whic