Metal-Insulator Transition in the Thiospinel CuIr2S4

Shoichi Nagata

《Chinese Journal of Physics》 43卷3S期 (2005/06) Pp. 722-735

並列摘要

The metal-insulator (M - I) transition in the thiospinel CuIr2S4 and the investigations related to this M - I transition have been extensively made in the last decade. This paper will present a brief survey of the M - I transition in CuIr2S4 and the other compounds with some chemical modifications of CuIr2S4. The spinel CuIr2S4 goes through a temperature-induced M - I transition at TM-I = 230 K with the structural transformation, at which a simultaneous bond-dimerization with spin-singlet state and charge-ordering transition takes place. The magnetic susceptibility exhibits a step-like anomaly at TM-I. Most noticeable characteristic is the absence of localized magnetic moment below TM-I. The monovalent state of Cu^+ ion at A-site has been verified, then the ionic state Cu^+Ir^+3Ir^+4S^2− 4 is realized in T ＜ TM-I, where Ir ions at B-site have mixed valence states of Ir+3 and Ir+4, where Ir^+3 is non-magnetic state with t2g^6 occupation. Recent exploration has revealed extensive evidence for a bond-dimerization. This bond-dimerization of Ir^+4 – Ir^+4 having S = 0 could be induced due to the Peierls instability mediated through the lattice. These results indicate that CuIr2S4 is a rare and unique example displaying a spin-dimerization transition although a three-dimensional compound.