A.c. susceptibility of melt-processed high Tc superconductors

Abstract

The force equilibrium equation including pinning, flux flow, flux creep and reversible flux line motion is used in order to calculate some properties of high T c superconductors connected with nonlinear flux diffusion. Some comparisons are made with experiments performed on melt-grown YBCO and melt-textured BSCCO as well as with results of the linear response theory. Our study shows that: (a) non-logarithmic relaxation is caused by flux flow; (b) interpretation of maxima in the imaginary part of a.c. susceptibility data as de-pinning lines seems to be questionable; (c) flux flow reduces the effects caused by the reversible flux line motion.