Abstract
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 Néel transition and a first-order Néel transition. The crossover line appears to emerge from a tricritical point that separates the first-order Néel transition from the second-order one. We argue that a valence jump occurs at the border of antiferromagnetism.
