METAL-INSULATOR TRANSITIONS IN BACO1-XNIXS2-Y

We report on the electrical and magnetic properties of the layered ternary sulfide system BaCo1-xNixS2-y. Ni doped samples of BaCoS2 that contain sulfur vacancies exhibit a first-order phase transition from a high temperature antiferromagnetic, semiconducting phase to a low temperature metallic phase. Increasing the sulfur vacancy concentration increases the Neel temperature of the two-dimensional antiferromagnetic phase and decreases the resistivity in the metallic phase. As the Ni content is increased, the system undergoes a smooth transition to a paramagnetic metal at all temperatures.