Compounds of the layered transition metal sulfide alloy series ${\mathrm{BaCo}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ni}}_{\mathit{x}}$${\mathrm{S}}_2$ were prepared. Structural, magnetic, and electrical properties were measured. These compounds consist of quasi-two-dimensional transition metal sulfur sheets separated by BaS rocksalt layers. With increasing Ni the ${\mathrm{BaCo}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ni}}_{\mathit{x}}$${\mathrm{S}}_2$ alloys change continuously from antiferromagnetic semiconductors to paramagnetic metals. The crossover in the electrical and magnetic properties both occur near x=0.25. The initial suppression of the Néel temperature with Ni substitution is characteristic of simple magnetic dilution in a quasi-two-dimensional Heisenberg antiferromagnet. The measured electrical and magnetic properties of the Ni-rich alloys are consistent with the calculated one-electron band structure of ${\mathrm{BaNiS}}_2$. The Co-rich alloys appear to be Mott-Hubbard insulators with electrical and magnetic properties very similar to those of ${\mathrm{La}}_2$${\mathrm{CuO}}_4$, the parent compound of the cuprate superconductors. © 1996 The American Physical Society.

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