Two-magnon light scattering in the layered antiferromagnet ${\mathrm{NiPS}}_3$: Spin-1/2-like anomalies in a spin-1 system

Raman spectra of ${\mathrm{NiPS}}_3$ (spin S=1) reveal an anomalously broad two-magnon feature whose relative width is comparable to that shown by ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ (S=1/2) and other antiferromagnetic copper oxides. The magnetic continuum is strongly coupled to a nearby phonon, whose scattering amplitude interferes with it. These results question the view that the width enhancement in the cuprates stems from large quantum fluctuations intrinsic to S=1/2 systems. It is proposed that the anomaly is due instead to magnon decay involving strong magnetostrictive coupling to phonons.