Pressure-induced magnetic order in golden SmS -: art. no. 066401

High pressure Sm-149 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(Delta)approximate to2 GPa 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(Delta). A Gamma(8) quartet crystal field ground state with a value of similar to0.5mu(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.