TB IMPURITIES IN TH - A KONDO SYSTEM WITH UNDERCOMPENSATED MAGNETIC-MOMENT

Dilute TbxTh1-x alloys have been thoroughly studied in the light of a possible valence instability and Kondo effect in Tb3+ and Tb4+ ions. W e review the experimental data for the specific heat, magnetic suscept ibility, magnetization, magnetoresistivity, and the change of the supe rconducting properties of Th. In analogy to Tm (Tm2+ and Tm3+) and Pr (Pr3+ and Pr4+) impurities in metals, Tb involves two electronic confi gurations each with a magnetic Hund's rule ground multiplet. Two class es of models for valence admixtures of two magnetic configurations hav e been investigated in the past. Depending on the form of the hybridiz ation and the jj coupling within the 4f shell, the models either have a singlet or a magnetic ground state. As for Tm impurities the latter class of models, related to the undercompensated Kondo effect, appears to describe the system TbTh more appropriately A qualitative explanat ion of the data is attempted within a scheme that combines Kondo scree ning with crystalline field splitting. (C) 1996 American Institute of Physics.