Valence transitions of Sm in monosulfide solid solutions

Abstract

Magnetic-susceptibility and lattice-parameter measurements indicate that Sm in ${\mathrm{Sm}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}\mathrm{S}$ for $xg0.15$, in ${\mathrm{Sm}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{S}$ for $xg0.33$, and in ${\mathrm{Sm}}_{1\ensuremath{-}x}{\mathrm{Gd}}_{x}\mathrm{S}$ for $xg0.17$ is in an intermediate valence state at $T=295$ K. A transition from this intermediate valence state to a more divalent but still intermediate valence state is observed on cooling and on heating from room temperature in ${\mathrm{Sm}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}\mathrm{S}$ for $0.15lxl0.27$. For $xg0.47$, Sm remains intermediate valent on cooling to $T=4.2$ K and on heating to $T=900$ K. Its susceptibility is independent of temperature below $T=100$ K. Related effects are observed in the ${\mathrm{Sm}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{S}$ and in the ${\mathrm{Sm}}_{1\ensuremath{-}x}{\mathrm{Gd}}_{x}\mathrm{S}$ systems. A model of interconfiguration fluctuations including multiple energy levels in both configurations and crystal-field effect may explain these results.