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 approximate to 2.5 K superconductivity coexists with weak ferromagnetism. We fmd that the critical currents are strongly enhanced for all field orientations in t his ferromagnetic regime, corresponding to a threefold increase of the pinn ing force of the flux line lattice. We speculate that this increase is due to strong pair breaking by the ferromagnetism.