A critical-state model for surface flux pinning in superconducting Pb-Na

Abstract
The AC response of a type II superconducting Pb-8.4 at.%Na single-crystal cylindrical rod with a (111) orientation in the mixed state is described and analysed when the specimen is in the surface pinning regime. The results show that flux entry is not mainly from the ends of the sample and a critical-state model is developed involving flux line entry along the sides of the specimen which is able to account satisfactorily for the experimental results. The frequency-dependent effects are also discussed and accounted for.

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