High-pressure synthesis and exotic heavy-fermion behaviour of the filled skutterudite SmPt4Ge12

Ternary samarium-filled platinum-germanium skutterudite SmPt4Ge12 was prepared at a pressure of 5.0(0.5)GPa and a temperature of 1070(70) K. The compound crystallizes in the cubic space group Im (3) over bar (a = 8.6069(4)angstrom) and is isotypic with LaFe4P12. X-ray absorption spectroscopy measurements show that samarium in SmPt4Ge12 has a temperature-independent intermediate valence (v=2.90 +/- 0.03). Magnetization data reveal Van Vleck paramagnetism above similar to 50 K. The low-temperature specific heat displays a broad anomaly centred at 2.9K and a large linear coefficient gamma'=450 mJ mol(-1) K-2 suggesting heavy-fermion behaviour. Low-temperature electrical resistivity shows a temperature dependence reminiscent of the Kondo effect. Density functional calculations result in an electronic structure that is, apart from the Sm 4 f contributions, very similar to LaPt4Ge12.