Superconducting and magnetic properties of filled skutterudite compounds RERu4Sb12 (RE=La, Ce, Pr, Nd and Eu)

We have studied superconducting and magnetic properties of RERu4Sb12 prepared by an Sb-flux method and found that LaRu4Sb12 is superconducting below 3.58 K and PrRu4Sb12 is a Van Vleck paramagnet which becomes superconducting below 1.04 K. CeRu4Sb12 is a unique substance which shows intermediate-valence behavior with a characteristic broad peak around 100 K in the magnetic susceptibility and Kondo-like behavior in the electrical resistivity at high temperatures. Furthermore, non-Fermi liquid behavior is observed in the specific heat and electrical resistivity at low temperatures. NdRu4Sb12 and EuRu4Sb12 show a magnetic transition at 1.3 K and 3.3 K, respectively.