Electronic transport and antiferromagnetism in the layered compound BaCoS2

BaCoS2 is a Mott insulator with a Neel temperature (7(N)) close to room temperature. In the ordered antiferromagnetic phase, the magnetic moments are confined in the Co2S2 planes, and arranged in alternatingly directed ferromagnetic chains. We report on resistivity and thermopower measurements and on room-temperature cell constants of samples of BaCoSz with nominal sulfur content 1.9 less than or equal to z less than or equal to 2.1. We discuss the effect of sulfur content on cell constants and band filling. The main observation is a crossover from activated electronic transport at high temperatures, to high resistivity almost independent of temperature, and accompanied by a vanishingly small thermopower, at low temperatures (far below T-N) We interpret the transport mechanism in the low-temperature regime as tunneling in the Co2S2 planes, to nearest neighbors along the ferromagnetic chains and to next-nearest neighbors in the perpendicular direction, or alternatively to nearest neighbors along the ferromagnetic chains with conducting inclusions acting as shorts. [S0163-1829(99)02410-8].