Phase diagrams and ground-state magnetic properties of Pr-based filled skutterudites

Phase diagrams and the ground-state magnetic properties of PrOs 4 Sb 12 , PrRu 4 P 12 and PrFe 4 P 12 are studied by means of low-temperature magnetization and specific heat measurements. Field-induced ordering observed in PrOs 4 Sb 12 for all directions above 4.5 T is well explained by a level crossing in the Γ 1 – Γ 4 ( T h ) pseudo-quartet states with inclusion of an antiferroquadrupolar (AFQ) interaction. In PrRu 4 P 12 , a Curie-like increase of the susceptibility observed down to below 300 mK indicates that a half of Pr 3 + ions have the magnetic Γ 4 ( T h ) triplet ground state, in accordance with a dramatic change in the crystal field splitting below the metal–insulator transition at 63 K recently observed by an inelastic neutron scattering experiment. In PrFe 4 P 12 , a new ordered phase is observed for H ( ∥ [ 1 1 1 ] ) > 7.5 T above the AFQ phase below 0.6 K, which is probably responsible for unusual heavy electron behavior observed in this field direction.