Kondo-like behavior near the magnetic instability in SmB6 : Temperature and pressure dependences of the Sm valence

We report a systematic study of Sm valence in the prototypical intermediate valence compound ${\mathrm{SmB}}_{6}$. Sm mean valence ${v}_{\mathrm{Sm}}$ was measured by x-ray absorption spectroscopy as a function of pressure $(1lPl13\phantom{\rule{0.28em}{0ex}}\mathrm{GPa})$ and temperature $(3lTl300\phantom{\rule{0.28em}{0ex}}\mathrm{K})$. Pressure-induced magnetic order was detected above ${P}_{c}=10\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$ by resistivity measurements. A shift toward the localized $4f$ state with increasing $P$ and/or $T$ is evident from an increase in ${v}_{\mathrm{Sm}}$. However ${v}_{\mathrm{Sm}}$ at ${P}_{c}$ is anomalously far below 3, which differs from the general case of nonmagnetic-magnetic transition in Yb and Ce compounds. From the $T$ dependence of ${v}_{\mathrm{Sm}}(P,T)$, we found that ${v}_{\mathrm{Sm}}(P,T)$ consists of two different characteristic components: One is associated with low-energy electronic correlations involving Kondo-like behavior, and the other is associated with high-energy valence fluctuations.