Impact of the Lattice on Magnetic Properties and Possible Spin Nematicity in the S = 1 Triangular Antiferromagnet NiGa 2 S 4

${\mathrm{NiGa}}_{2}{\mathrm{S}}_{4}$ is a triangular lattice $S=1$ system with strong two dimensionality of the lattice, actively discussed as a candidate to host spin-nematic order brought about by strong quadrupole coupling. Using Raman scattering spectroscopy we identify a phonon of ${E}_{g}$ symmetry which can modulate magnetic exchange ${J}_{1}$ and produce quadrupole coupling. Additionally, our Raman scattering results demonstrate a loss of local inversion symmetry on cooling, which we associate with sulfur vacancies. This will lead to disordered Dzyaloshinskii-Moriya interactions, which can prevent long-range magnetic order. Using magnetic Raman scattering response we identify 160 K as a temperature of an upturn of magnetic correlations. The temperature range below 160 K, but above 50 K where antiferromagnetic correlations start to increase, is a candidate for spin-nematic regime.