NEW DENSE KONDO SYSTEMS CE3PD20GE(SI)(6) AND RELATED-COMPOUNDS SM(YB)(3)PD20GE(SI)(6)

The electrical and magnetic properties of a new cubic system Ln(3)PD(2 0)X(6) (Ln=Ce, Sm, Yb; X=Si, Ge) have been studied. The electrical res istivity rho versus temperature shows a minimum at similar to 50 K for Ce3Pd20Si6, and at similar to 10 K for Ce3Pd20Ge6. Below these temper atures rho(T) follows a logarithmic law down to 4.2 K. In Ce3Pd20Si6 t he thermal behavior of the magnetic moment displays an antiferromagnet ic anomaly at approximately 50-60 K and marked 'superparamagnetic' pro perties on further cooling. To explain the unusual magnetic behavior o f Ce3Pd20Si6 a model of 'molecular' magnetism is suggested for one of two cerium sublattices. Another cerium subsystem is likely to respond for Kondo anomalies. In contrast with cerium compounds, the samarium a nd ytterbium homologues display normal metallic behavior with a nonmag netic ground state down to 4.2 K.