Synthesis and Properties of Cobalt Sulfide Phases: CoS2 and Co9S8

Single phase cobalt disulfide (CoS2) nanoparticles were prepared by thermal decomposition of cobalt-thiourea complex at a low temperature (400 degrees C). CoS2 nanoparticles exhibit ferromagnetic ordering at 122 K below which the temperature dependent resistivity of cold pressed nanoparticles deviates from metallic behavior and shows a broad maximum. Just below T-C, it also exhibits a large magnetoresistance effect (6.5%). A mixture of CoS and Co9S8 phases were obtained between the temperature interval 400 degrees C < T < 1000 degrees C. At 1000 degrees C, a pure bulk Co9S8 phase was obtained. It exhibits magnetic hysteresis typical of a ferromagnet at room temperature and a peak in magnetization at low temperature with a strong relaxation indicating possible spin glass state.