The critical current density Jc has been measured for superconductornormal- metalsuperconductor (S-N-S) junctions over a wide range of temperature and composition in order to determine the depairing effects of magnetic impurities. Junctions, which are in a sandwich geometry with the N layer typically 600 nm thick, show well-defined diffraction patterns indicating that the junctions are of high quality. Below 4.2 K, the temperature dependence of Jc is found to follow a modified bridge theory based on the work of Makeev et al. (Fiz. Nizk. Temp. 6, 429 (1980) [Sov. J. Low Temp. Phys. 6, 203 (1980)]). In this range, the coherence length and order parameter in the superconductor are essentially independent of temperature, and so it is reasonable that the bridge and sandwich geometry results are similar. As the temperature approaches the transition temperature (TcS) of the superconductor, Jc was found to be proportional to (1-TTcS)2 as predicted by de Gennes.
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