We have investigated the anisotropy of the magnetoresistance in the Pr-based HF compound PrFe4P12. The large anisotropy of effective mass and its strong field dependence have been confirmed by resistivity measurements. Particularly for H||[111], wher
e the effective mass is most strongly enhanced, the non-Fermi liquid behavior has been observed. Also, we have found the angular dependence of the magnetoresistance sharply enhanced at H||[111], which is evidently correlated with both the non-Fermi liquid behavior and the high-field ordered state (B-phase).
We report on systematic study of superconducting characteristics and Pr crystalline-electric-field (CEF) levels of filled-skutterudite pra ($T_{rm c}$ = 2.33 K). The temperature dependences of the upper critical field $H_{rm c2}$ and the Ginzburg-Lan
dau (Maki) parameter $kappa_2$ suggest an s-wave clean-limit superconductivity. The electronic specific heat coefficient $gamma sim 95$ mJ/K$^2$mol, being $sim 1.5$ times larger than that for lra, indicates $4f$-originating quasiparticle mass enhancement. Magnetic susceptibility $chi(T)$ indicates that the CEF ground state is a $Gamma_1$ singlet and a $Gamma_4^{(1)}$ triplet first excited state lies at $Delta_{rm CEF}sim 30$ K above. Systematic comparison among pos, prs, pra and La-based reference compounds suggests that inelastic exchange- and aspherical-charge-scatterings of conduction electrons from CEF-split $4f$ levels play an essential role for the quasiparticle mass enhancement and the value of $T_{rm c}$ in the Pr-based filled skutterudites.
