Electrical, Magnetic and NMR Studies of Ge-Based Filled Skutterudites <i>R</i>Pt₄Ge₁₂ (<i>R</i>=La, Ce, Pr, Nd)

Abstract

We have synthesized the polycrystalline samples of Ge-based filled skutterudites R Pt 4 Ge 12 ( R =La, Ce, Pr, Nd) and investigated the lattice constant, electrical resistivity, magnetic susceptibility and nuclear magnetic resonance (NMR) systematically. LaPt 4 Ge 12 is confirmed to be a conventional BCS-type superconductor by the NMR measurements. Additional contribution ascribed to the rattling motion of the La ions has been observed in the nuclear relaxation at the La site at high temperatures. Temperature dependence of the magnetic susceptibility of CePt 4 Ge 12 shows a broad peak around 80 K, which is a typical feature of valence fluctuation systems, whereas PrPt 4 Ge 12 and NdPt 4 Ge 12 show the well-localized nature of 4 f -electrons. The NMR measurements in CePt 4 Ge 12 revealed that the nuclear spin–lattice relaxation rate 1/ T 1 shows an activation-type temperature dependence 1/ T 1 ∝exp (-Δ/ k B T ) with an energy gap Δ/ k B =150 K above 100 K, whereas it is proportional to the temperature below 20 K. This behavior is explained by a pseudogap model originated by the c – f hybridization.