KINETICS OF MAGNETIC-RELAXATION AND DETERMINATION OF ACTIVATION-ENERGY IN HIGH-TC SUPERCONDUCTORS

The deviation of magnetic relaxation from the usual logarithmic decay in type-II superconductors was analyzed in terms of the first-order ki netic relaxation process. The theoretical and experimental results sho w that the relaxation of magnetic induction B obeys the power law equa tion, namely, B = B0 + B1t(-alpha), where B0 is the ''equilibrium'' va lue of the magnetic induction, and B1 and alpha are field- and tempera ture-dependent constants. It was found that alpha, which is related to the pinning potential barrier, varies with temperature following the Arrhenius-type thermal activation behavior. Based on the present pheno menological theory, the current J dependence of the apparent activatio n energy U(a) is discussed by using the relaxation data of a Bi2.1Sr1. 8Ca1.0Cu2.0O8+delta single crystal.