Metal-insulator transition in the spinel-type Cu1-xNixIr2S4 system - art. no. 075106

The normal thiospinel CuIr2S4 exhibits a temperature-induced metal-insulato r (M-1) transition around 230 K with structural trans form ati on, showing hysteresis on heating and cooling. The symmetry changes from a high-tempera ture cubic phase in a metallic state to low-temperature tetragonal phase in an insulating state. A significant characteristic feature is the absence o f localized magnetic moment below TM-1. On the other hand, NiIr2S4 remains metallic down to 4.2 K without the structural transformation. We have syste matically studied the structural transformation and electrical and magnetic properties of Cu1-xNixIr2S4. The variation of the metal-insulator transiti on with Ni concentration x is presented. A phase diagram between TM-1 and x will be provided for the Cu1-xNixIr2S4 system. The TM-1 varies drastically from 226 to 88 K with x from 0.00 to 0.13 and disappear, around x = 0.15. For 0.08 less than or equal tox less than or equal to0.13, the cubic and te tragonal phases coexist below TM-1. For a high-temperature metallic phase, the value of the Pauli paramagnetic susceptibility increases monotonically with x, which shows dD(epsilon)/d epsilon <0 at the Fermi energy <epsilon>( F), through the decrease of the free-electron number density, where D(epsil on) is the electronic density-of-state on the basis of a nearly free-electr on model. By the introduction of a Ni ion to the A-site of CuIr2S4 in the s pinel structure, whether the localized magnetic moment below TM-1 arises or not will be discussed.