Absence of magnetic ordering in NiGa_2S_4

TL;DR

This study investigates the magnetic properties of NiGa2S4, revealing that it does not develop magnetic order down to low temperatures, with calculations showing specific exchange interactions and their suppression by electron correlations.

Contribution

First principles calculations elucidate the exchange interactions in NiGa2S4, explaining the absence of magnetic order despite its layered triangular structure.

Findings

Second neighbor exchange is negligible

First and third neighbor exchanges are comparable and antiferromagnetic

Exchange interactions are suppressed by Hubbard repulsion

Abstract

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 end 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.