Charge and magnetic ordering in mixed valence system Sm₄(Bi_1-xSb_x)3

The mixed valence compound Sm₄Bi₃ shows the charge ordered state of Sm²⁺ and Sm³⁺ with a ratio of 3:1 and its behavior is similar to that of well-known compound Yb₄As₃. The main interest in Sm₄Bi₃ is a pressure-induced iso-structural transition from a mixed valence state to a trivalent state, in which physical properties are very similar to that of Sm₄Sb₃. To reproduce the high-pressure phase, we synthesized and investigated Sm₄(Bi_1-xSb_x)₃ system. With increasing Sb content, the carrier concentration decreases and the charge ordering temperature slightly increases, while by applying pressure the ordering temperature decreases. These relationships between the substitution and pressure effect in Sm₄Bi₃ is very similar to that in Yb₄As₃. So, it may be suggested that Sm₄Bi₃ is a semimetal in the same way as the case of Yb₄As₃. The substitution effect may be different from the pressure effect though both effects finally lead to a trivalent state.