Enhanced critical currents of superconducting erni₂b₂c in the ferromagnetically ordered state

We report on transport and magnetization studies of the critical current in single crystal ErNi₂B₂C for applied fields below 4 kG. Below T≈2.5 K superconductivity coexists with weak ferromagnetism. We find that the critical currents are strongly enhanced for all field orientations in this ferromagnetic regime, corresponding to a threefold increase of the pinning force of the flux line lattice. We speculate that this increase is due to strong pair breaking by the ferromagnetism.