Detailed heat capacity measurements of the ternary compounds ErRh4B~ and LuRh,d34 have been performed between 0.5 and 36 K and in magnetic fields up to 4 kG, yieMing new information on crystal fieM effects in these materials and on the influence of externally applied magnetic fields on the coupled superconducting-ferromagnetic reentrant transition in ErRh4B4. Static magnetic susceptibility data on LuRh4B4 are presented which allow qualitative conclusions to be drawn regarding the magnitude of exchange enhancement and orbital paramagnetic effects in the RURh4B~ compounds. The electrical resistivity of ErRh4B4 has also been determined between 4 K and room temperature.
1. Introduction
Recently a series of primitive tetragonal rare earth (RE) compounds with the formula t RERh4B4 were reported by Matthias et al. to become either superconducting or ferromagnetic, z Whereas the Gd, Tb, Dy, and Ho members of the series were found to exhibit ferromagnetism, the Nd, Sin, Er, Tin, and Lu members were reported to become superconducting. Fertig et al. 3 subsequently showed that following the transition from the normal state to the superconducting state at Tel = 8.7 K in ErRhaB4, a thermally hysteretic superconducting to normal state transition occurred at To2 0.9 K. The transition at Tcz was ascribed to the long-range ordering of the