Point-contact study of the magnetic superconductor HoNi2B2C

Point contacts (PC) based on the magnetic superconductor HoNi2B2C with a su perconducting onset temperature T-c similar to 8.5 K have been investigated in order to determine the temperature and magnetic field dependences of th e superconducting order parameter. The temperature dependence of the order parameter satisfies the Bardeen-Cooper-Schrieffer (BCS) theory only below t he BCS transition temperature T-c(BCS) = 55-5.8 K, which exceeds slightly t he Neel temperature T-N similar to 5.0 K. At higher temperatures, above T-N , the PC spectra dV/dI(V) indicate an anomalous, most likely gapless, super conducting state. At magnetic fields well below H-c2, a considerable increa se (similar to 30%) in the characteristic voltage of the gap-related struct ure in the PC spectra is observed which points to an improved spin alignmen t with a decreasing influence of the pair breaking in modest fields. (C) 19 99 Elsevier Science B.V. All rights reserved.