Weak links as a subsystem that monitors the intragranular flux creep in high-Tcsuperconductors

The time dependence of the dc voltage that remains on a sintered ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{x}}$ sample after the application of a magnetic field has been systematically studied in various magnetic fields and at three different temperatures. The obtained logarithmic time dependence has been related to the intragranular flux creep assuming that the dissipative part of the sample, the subsystem of weak links, is controlled by local magnetic fields. A one-dimensional model for the dissipation has been introduced and solved numerically, showing that the inverse of the relaxation rate approaches the intragranular pinning potential in the limit of high applied fields. The experimental values of appropriately defined pinning potentials increases with temperature.