Magnetic Phase Diagram and Metal-Insulator Transition of NiS2-xSex

Magnetic phase diagram of NiS2-xSex has been reexamined by systematic studies of electrical resistivity, uniform magnetic susceptibility and neutron diffraction using single crystals grown by a chemical transport method. The electrical resistivity and the uniform magnetic susceptibility exhibit the same feature of temperature dependence over a wide Se concentration. A distinct first order metal-insulator (M-I) transition accompanied by a volume change was observed only in the antiferromagnetic ordered phase for 0.50<x<0.59. In this region, the M-I transition makes substantial effects to the thermal evolution of staggered moments. In the paramagnetic phase, the M-I transition becomes broad; both the electrical resistivity and the uniform magnetic susceptibility exhibit a broad maximum around the temperatures on the M-I transition-line extrapolated to the paramagnetic phase.