Nonmagnetic4fShell in the High-Pressure Phase of SmS

The magnetic susceptibility of SmS indicates a discontinuous and hysteretic magnetic transition at 6 kbar. The ground state of the $4f$ shell in the metallic high-pressure "collapsed" phase is nonmagnetic, contrary to Hund's rules. Nonmagnetic behavior of the $4f$ shell is correlated with an intermediate valence in SmS, Sm${\mathrm{B}}_6$, and $\alpha -\mathrm{Ce}$. It is suggested that in such intermediate-valence phases at $T=0\mathrm{}$ the $4f$ shell is demagnetized in the sense of the Friedel-Anderson model as modified by Hirst.