A spike-shaped heat-capacity anomaly has been identified at the lower superconducting-to-normal transition temperature $T_{c2\mathrm{}}$ of the magnetic superconducting system (${\mathrm{Er}}_{1-x}{\mathrm{Ho}}_x$)-${\mathrm{Rh}}_4$${\mathrm{B}}_4$. This anomaly can be distinguished from the feature due to long-range magnetic ordering and indicates that the transition at $T_{c2\mathrm{}}$ is thermodynamically of first order.

• Received 29 January 1979

DOI:https://doi.org/10.1103/PhysRevLett.42.918