Magnetism and superconductivity in the system ${\mathrm{Ce}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{La}}_{\mathrm{x}}$${\mathrm{Rh}}_3$${\mathrm{B}}_2$

The compound ${\mathrm{CeRh}}_3$ ${\mathrm{B}}_2$ is magnetically ordered with a low saturation moment of ∼0.4 ${\mu }_B$ per formula unit and an unusually large Curie temperature of 115 K while isostructural ${\mathrm{LaRh}}_3$ ${\mathrm{B}}_2$ is superconducting with a transition temperature of ∼2.3 K. Magnetic and superconducting studies on the series of compounds ${\mathrm{Ce}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{La}}_{\mathrm{x}}$ ${\mathrm{Rh}}_3$ ${\mathrm{B}}_2$ reveal that the magnetic state persists for 0≤x≤0.8. The magnetic moment per Ce ion goes through a maximum and the Curie temperature decreases as La is substituted for Ce. On the La-rich side, superconductivity is destroyed even with 1% replacement of La by Ce, indicating a strong coupling of Ce 4f moments with conduction-electron spins. The temperature dependence of the upper critical field of ${\mathrm{LaRh}}_3$ ${\mathrm{B}}_2$ has been measured and is discussed in terms of Werthammer-Helfand-Hohenberg theory.