Ab initio investigation of magnetic interactions in the frustrated triangular magnet NiGa₂S₄

Triangular-layered NiGa₂S₄, contrary to intuitive expectation, does not form a noncollinear antiferromagnetic structure, as do isoelectronic NaCrO₂ and LiCrO₂. Instead, the local magnetic moments remain disordered down to the lowest measured temperature. To get more insight into this phenomenon, we have performed first principles calculations of the first, second, and third neighbors exchange interactions, and found that the second neighbor exchange is negligible, while the first and the third neighbor exchanges are comparable and antiferromagnetic. Both are rapidly suppressed by the on-site Hubbard repulsion.