The suppression of the orbit-induced Peierls state by Co ions in the CuIr2-xCoxS4 system

The orbit-dependent hopping of the 5d shell electrons of Ir4+ ions is used to explain the Peierls-like phase transition in the sulphide CuIr2S4 system. This orbit-induced Peierls state can be suppressed by the substitution of Co ions with smaller splitting energy ΔEdγ-dɛ at the center of BS6 octahedron for Ir ions, and the metallic state is enhanced due to the increase of itinerant electrons with the increase of Co content in CuIr2-xCoxS4 system. The specific heat for CuIr2-xCoxS4 system is also investigated. The contribution of the electron specific heat becomes important at low temperatures with the increase of Co content, and the Cp/T-T2 relation at low temperatures deviates from the straight line with the increase of Co content, which is due to the scattering of the electrons by the magnetic moments at low temperatures.