Metal-Insulator Transition and Itinerant Antiferromagnetism
in NiS_2-xSe_x Pyrite

Abstract

The bandwidth-controlled metal-insulator (MI) transition in pyrite-type NiS_2-xSe_x has been investigated. The results indicate that the approach to the MI transition from the metallic side is profoundly affected by the presence of the antiferromagnetic metal (AFM) phase (0.4<x<1.0) immediately next to the MI phase boundary. In the paramagnetic metal (PM) phase (1.0<x≤2.0), the approach is simply characterized by mass enhancement. In the AFM phase, however, the approach is driven by a marked decrease in the carrier density on approaching the insulating phase.