Low-frequency a.c. susceptibility of a superconducting Pb–Sn eutectic alloy

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Abstract
The experimentally determined a.c. susceptibility is not explained by the critical surface state or effective conductivity models. A simple quasistatic model, valid in both static and swept d.c. fields, is developed which implicitly takes into account contributions to surface hysteresis. The model is in reasonable agreement with experimental results and is in accord with the observed magnetization curve. The magnetization and a.c. susceptibility show that flux motion through the surface is sensitive to the sense of the applied field change. This is not explained by the available flux creep models but is in accord with surface rectification effects. In view of the pinning centres in the surface region this seems reasonable.