Superconductivity, crystal-field effects, and magnetic order in the (Sm1−xYx)Rh4B4mixed ternary system

The phase diagram of the superconducting transition temperature $T_c$ and the magnetic ordering temperature $T_M$ versus the composition x has been determined for the mixed ternary system (${\mathrm{Sm}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Y}}_{\mathrm{x}}$)${\mathrm{Rh}}_4$ ${\mathrm{B}}_4$. The x dependence of $T_c$ is described well by the Abrikosov-Gor’kov theory modified to include the influence of the crystalline electric field on the ${\mathrm{Sm}}^{3+}$ ions. Heat-capacity measurements show that $T_M$ decreases linearly with x at the rate ${\mathrm{dT}}_M$/dx=-0.0128 K/(at. % Y). The influence of this magnetic order on superconductivity suggests that a transition from antiferromagnetism to ferromagnetism takes place for x∼0.4.