New dense Kondo systems Ce 3Pd 20Ge(Si) 6 and related compounds Sm(Yb) 3Pd 20Ge(Si) 6

Abstract

The electrical and magnetic properties of a new cubic system Ln 3Pd 20X 6 (Ln = Ce, Sm, Yb; X = Si, Ge) have been studied. The electrical resistivity ρ versus temperature shows a minimum at ∼ 50 K for Ce 3Pd 20Si 6, and at ∼ 10 K for Ce 3Pd 20Ge 6. Below these temperatures ρ( T) follows a logarithmic law down to 4.2 K. In Ce 3Pd 20Si 6 the thermal behavior of the magnetic moment displays an antiferromagnetic anomaly at approximately 50–60 K and marked ‘superparamagnetic’ properties on further cooling. To explain the unusual magnetic behavior of Ce 3Pd 20Si 6 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 and ytterbium homologues display normal metallic behavior with a nonmagnetic ground state down to 4.2 K.