Zusammenfassung
Typical phenomena and current concepts of rare earth (RE) ions in metals
are briefly reviewed. As an exemplary host, the superconductor LaAl 2
was chosen to delineate the magnetic behavior of the `normal' RE Gd and
Tb and of the `ambivalent' RE Ce. Since magnetic interactions between RE
ions are found to be extremely weak, relevant aspects of single ion
behavior can be studied with high accuracy. The properties of the
`normal' RE reflect the ferromagnetic exchange interaction with the
conduction electrons and the coupling to the crystalline electric field
(CF). The behavior of the `ambivalent' Ce is dominated by covalent
mixing of the 4f states with the conduction band states. Modification of
this interaction by lattice pressure, and its competition with CF
effects and magnetic interactions are discussed.
