New aspects of electronic ordered states due to f ² configuration of Pr-based systems

Strong hybridization between conduction electrons and f ² electrons in a trivalent Pr ion is a recent attractive subject. For example, the Pr-filled skutterudite compounds have been extensively studied. Pr(Ru _1-xRh _x) ₄P ₁₂ exhibits the reentrant-like behavior of the metal-nonmetal transition, and PrFe ₄P ₁₂ the heavy-fermion state followed by the nonmetallic ordering. In this article, we review briefly these phenomena characterized by the staggered structures of the totally symmetric order parameters of f ² state. We also demonstrate the higher-order magnetic scattering of polarized neutron to investigate quantum state levels in the f electron systems, which is expected to be carried out at the pulsed neutron facility J-PARC MLF.