  We measured the thermal expansion of the valence fluctuating phase of SmS
(golden SmS) to construct a pressure vs temperature phase diagram. The obtained
phase diagram is characterized by three lines. One is a crossover line that
divides the paramagnetic phase into two regions. The other two lines correspond
to a second-order Neel transition and a first-order Neel transition. The
crossover line appears to emerge from a tricritical point that separates the
first-order Neel transition from the second-order one. We argue that a valence
jump occurs at the border of antiferromagnetism.
