VORTEX DYNAMICS DURING N-S AND S-N TRANSITIONS OF Y-BA-CU-O SUPERCONDUCTORS UNDER THE EFFECT OF TEMPERATURE-GRADIENT AND THERMAL CYCLING

AC susceptibility of ac has been measured simultaneously in three diff erent ran Y-Ba-Cu-O ceramic samples in the presence of a large and var iable temperature gradient, The results obtained for normal-supercondu cting or superconducting-normal transitions under the effect of the on e-dimensional nonequilibrium temperature distribution reveal the vorte x motion to consist of not only conventional Aux expulsion (Or flux pe netration), but flux exchange too, appearing between different ranges of samples and between samples and their close physical environment. T he thermal cycles are shown to represent a supplementary heat treatmen t, increasing the homogeneity of the sample and decreasing the pinning , which accelerate the process of vortex motion.