We report the effect of $\alpha$-particle irradiation on the reduction of the critical temperature $T_c$ of a NdFeAs(OF) single crystal. Our data indicate that irradiation defects cause both nonmagnetic and magnetic scattering, resulting in the Kondo-like excess resistance $\Delta \rho (T)\propto \ln T$ over 2 decades in temperatures above $T_c$. The critical density of magnetic irradiation defects which suppresses $T_c$ is found to be much higher than those for cuprates and multiband BCS superconductors. We suggest that such anomalously weak pair breaking by irradiation defects indicates that magnetic scattering in pnictides is coupled with pairing interactions mediated by spin fluctuations.

• Received 6 October 2009

DOI:https://doi.org/10.1103/PhysRevLett.104.087002