Magnetism and superconductivity in the systemCe1−xLaxRh3B2

The compound ${\mathrm{CeRh}}_{3}$${\mathrm{B}}_{2}$ is magnetically ordered with a low saturation moment of \ensuremath{\sim}0.4 ${\ensuremath{\mu}}_{B}$ per formula unit and an unusually large Curie temperature of 115 K while isostructural ${\mathrm{LaRh}}_{3}$${\mathrm{B}}_{2}$ is superconducting with a transition temperature of \ensuremath{\sim}2.3 K. Magnetic and superconducting studies on the series of compounds ${\mathrm{Ce}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{La}}_{\mathrm{x}}$${\mathrm{Rh}}_{3}$${\mathrm{B}}_{2}$ reveal that the magnetic state persists for 0\ensuremath{\le}x\ensuremath{\le}0.8. The magnetic moment per Ce ion goes through a maximum and the Curie temperature decreases as La is substituted for Ce. On the La-rich side, superconductivity is destroyed even with 1% replacement of La by Ce, indicating a strong coupling of Ce 4f moments with conduction-electron spins. The temperature dependence of the upper critical field of ${\mathrm{LaRh}}_{3}$${\mathrm{B}}_{2}$ has been measured and is discussed in terms of Werthammer-Helfand-Hohenberg theory.