Observation of itinerant ferromagnetism and coupled magnetoresistance in a spinel CuCo₂S₄

We report the existence of ferromagnetism in the thiospinel compound CuCo₂S₄withT_c∼ 125 K. The magneto-electronic transport of the CuCo₂S₄demonstrates 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 CuCo₂S₄was calculated using density-functional theory (DFT), which shows a ferromagnetic metallic state, in agreement with experiment. With nickel doping, both the spinel CuCo_1.5Ni_0.5S₄and CuCoNiS₄display 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.