Observation of itinerant ferromagnetism and coupled magnetoresistance in a spinel CuCo2S4

We report the existence of ferromagnetism in the thiospinel compound CuCo2S4 with T-c similar to 125 K. The magneto-electronic transport of the CuCo2S4 demonstrates a metallic conductivity and positive magnetoresistance at high temperature. At low temperature, in the ferromagnetic state, there is evidence of spin-transport coupling with magnetic domains giving a region of negative magnetoresistance near the coercive field. The electronic band structure of CuCo2S4 was calculated using density-functional theory (DFT), which shows a ferromagnetic metallic state, in agreement with experiment. With nickel doping, both the spinel CuCo1.5Ni0.5S4 and CuCoNiS4 display paramagnetism down to the lowest measured temperature (3 K). This indicates that, as in other itinerant magnetic sulfides, the exchange interactions are highly sensitive to electron/hole doping. The tunable magnetism in the spinel CuCo2S4, together with its high conductivity, suggests that this thiospinel material could be a candidate for spintronic applications.