Pressure-Induced Magnetic Order in Golden SmS

Abstract

High pressure $^{149}\mathrm{S}\mathrm{m}$ nuclear forward scattering experiments have been performed on the nonmagnetic semiconductor SmS. We present the first clear evidence that the closure of the insulating gap at ${p}_{\mathrm{\ensuremath{\Delta}}}\ensuremath{\approx}2\text{ }\text{ }\mathrm{G}\mathrm{P}\mathrm{a}$ coincides with the appearance of magnetic order. The pressure-induced magnetic phase transition has some first order character and suggests that the Sm ions are nearly trivalent at ${p}_{\mathrm{\ensuremath{\Delta}}}$. A ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{8}}$ quartet crystal field ground state with a value of $\ensuremath{\sim}0.5{\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$ for the samarium magnetic moment is inferred from our results. Considerable magnetic short range order is observed above the ordering temperature inferred from macroscopic measurements.