Nonmagnetic Ground State in Fully Filled PrxFe4Sb12 (x=1.0) Synthesized under High Pressure

We have succeeded in synthesizing the filled skutterudite Pr x Fe 4 Sb 12 with the Pr-site filling fraction x close to 1 under high pressure. The residual resistivity of ∼24 µΩ·cm is several times smaller than that of samples with x ∼0.8 synthesized under ambient pressure by independent research groups, indicating that highly improved sample quality can be achieved by reducing the Pr-site vacancy. From the transport, magnetic, and thermal measurements of the present sample with x ∼1, we have found a singlet ground state of the crystalline electric field (CEF) for 4 f -electrons and no phase transition down to 0.15 K, in contrast to the reported magnetic ordering near 5 K in the samples with x ∼0.8. The effect of the Pr-site vacancy on the CEF level scheme and the 3 d -electron density of states near the Fermi level is discussed as a possible origin of such a drastic change in the magnetic ground state.