Magnetic and transport properties of electron-doped BaCoS2: Coexistence ofantiferromagnetism and metallic conductivity

The layered compounds Ba1-xBixCoS2 (0 less than or equal to x less than or equal to 0.7) were prepared in a single phase of the BaCoS2 type. The elect ric resistivity was found to be drastically decreased with x and shows a sy stematic change from insulating to metallic with decreasing temperatures: t he electric resistivity for x greater than or equal to 0.05 follows the T-2 -dependence below 20K, indicating that the Fermi liquid state is realized a t low temperatures, while it shows semiconducting temperature dependence at high temperatures. The electronic specific heat coefficient gamma for Ba0. 95Bi0.05CoS2 was estimated to be a small value of 3.5 mJ/mol.K-2 instead of the large T-2-term in the resistivity. In magnetic susceptibility measurem ents, the antiferromagnetic ordering was found to be stable even in metalli c samples. These results can be understood as: two types of electronic hand s near the Fermi level in the electron-doped BaCoS2, one of which has the M ott-Hubbard gap giving rise to the antiferromagnetic ordering just as BaCoS 2 and the other has a small but finite size of density of states at the Fer mi level; sho\iring metallic conduction.