Pressure dependence of magnetic excitations in SmS

Abstract

Inelastic-neutron-scattering studies using triple-axis and time-of-flight techniques have been made in the low- and high-pressure phases of a polycrystalline sample of $^{154}\mathrm{Sm}$S. There is no observable change in the energy or width of the $^{7}F_{0}\ensuremath{-}^{7}F_{1}$ excitation of the $4{f}^{6}$ configuration between ambient pressure and 0.6 GPa. In the mixed-valence phase at high pressure, there is no evidence for well-localized excitations from either the $^{7}F_{0}\ensuremath{-}^{7}F_{1}$ ($4{f}^{6}$) or the ${\ensuremath{\Gamma}}_{7}\ensuremath{-}{\ensuremath{\Gamma}}_{8}(^{6}H_{\frac{5}{2}}, 4{f}^{5})$ configurations. These results suggest that the mixed-valence phase is homogeneous. Lattice-parameter measurements versus pressure at 85 and 298 K show no evidence for pretransitional softening and establish that the phase diagram in the $P\ensuremath{-}T$ plane is reentrant. From the phase diagram and earlier heat-capacity measurements, the electronic entropy in the mixed-valence phase is estimated to saturate at $\ensuremath{\simeq}2R$ with increasing temperature.