Transport, Thermal and Magnetic Properties of the New Ternary Compound U3Pd20Si6: Possibility of a New Localized5fElectrons System

We have succeeded in growing the single crystal of a new ternary intermetallic uranium compound U 3 Pd 20 Si 6 . It crystallizes in the Cr 23 C 6 -type cubic structure and the uranium ions are located on two different crystallographic sites. Two sucessive magnetic phase transitions are found at 19 K and 2 K in the electrical resistivity, specific heat and magnetic susceptibility measurements. These are attributed to antiferromagnetic and ferromagnetic orderings, respectively. The magnetic susceptibility obeys the Curie-Weiss law above about 50 K with the effective moment 3.30 µ B /U and the magnetic entropy at 19 K is about R ln 3 per uranium ion. These results indicate that the 5 f electrons in U 3 Pd 20 Si 6 are likely to be localized. We discuss the magnetic properties of U 3 Pd 20 Si 6 in comparison with those of R 3 Pd 20 X 6 (R=rare earth: X= Si, Ge).