Metal-insulator transition and superconductivity in the spinel-type Cu(Ir1−xRhx)2S4 system

Abstract

The normal thiospinel CuIr2S4 exhibits a temperature-induced metal-insulator (M−I) transition around 226 K with structural transformation, showing hysteresis on heating and cooling. It has been verified that d electrons of Ir atom on the octahedral B sites have a significant role for the M−I transition. On the other hand, CuRh2S4 is a superconductor with the transition temperature Tc=4.70 K, which is well understood on the basis of the BCS theory. It is important to investigate the effect on the M−I transition by substitution of Rh for Ir. We have systematically studied structural transformation and electrical and magnetic properties of Cu(Ir1−xRhx)2S4. The features of the M−I transition change with Rh concentration x. A phase diagram of temperature versus x will be proposed for the Cu(Ir1−xRhx)2S4 system. The sharp M−I transition temperature varies drastically from 226 to 93 K with x from 0.00 to 0.17 and disappears around x=0.20. In a region of 0.00<~x<~0.20, the magnetic susceptibility begins decreasing at a constant onset temperature 226 K on cooling process and shows rather broad temperature variation, even though the metallic state is kept in the resistivity. The sharp M−I transition can take place after the suppression of magnitude in the susceptibility has sufficiently developed far below 226 K. These experimental results are discussed with emphasis on the intrinsic difference between Cu(Ir1−xRhx)2S4 and CuIr2(S1−xSex)4 systems. Furthermore, we will mention the superconductivity for both systems of Cu(Ir1−xRhx)2S4 with high-Rh concentration region and Cu1−xNixRh2S4.

Source-reported materials — not catalogue approval

Similar papers