Metal–Insulator Transition of Filled Skutterudite Compound SmRu₄P₁₂

Abstract

Filled skutterudite SmRu 4 P 12 exhibits a metal–insulator (M–I) transition near 16 K (= T MI ). We have measured in detail the specific heat C ( T ), electrical resistivity ρ( T ) and magnetization M ( T ) under high magnetic field around M–I transition. The detailed measurements have revealed that this M–I transition is caused by two successive transitions. The single peak in C ( T ) at zero field changes into a double peak with increasing field. (-dρ/d T ) and d M /d T exhibit two anomalies at almost the same positions as the specific heat peaks. The magnetic entropy estimated at zero field reaches R ln 4 below T MI . The crystalline electric field (CEF) ground state is a quartet in cubic symmetry. It is suggested that the M–I transition of SmRu 4 P 12 is related to an orbital ordering originating from the CEF ground state quartet.