Vortex dynamics during N–S and S–N transitions of Y–Ba–Cu–O superconductors under the effect of temperature gradient and thermal cycling

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AC susceptibility of ac has been measured simultaneously in three different ranges of Y–Ba–Cu –O ceramic samples in the presence of a large and variable temperature gradient. The results obtained for normal-superconducting or superconducting-normal transitions under the effect of the one-dimensional nonequilibrium temperature distribution reveal the vortex motion to consist of not only conventional flux expulsion (or flux penetration), but flux exchange too, appearing between different ranges of samples and between samples and their close physical environment. The thermal cycles are shown to represent a supplementary heat treatment, increasing the homogeneity of the sample and decreasing the pinning, which accelerate the process of vortex motion.