LOCAL MAGNETIC-RELAXATION IN HIGH-TEMPERATURE SUPERCONDUCTORS

A novel Hall probe array technique is used to measure the spatial dist ribution and time dependence of the magnetic induction in YBa2Cu3O7-de lta crystals. Analysis of the data based on the flux diffusion equatio n allows a direct, model-independent determination of the local activa tion energy U and the logarithmic time scale to for flux creep. The re sults indicate that the spatial variations of U are small (+/-kT) and that U increases logarithmically with time. The time t(0) is inversely proportional to the field and it exhibits a nonmonotonic temperature dependence. These results confirm theoretical predictions based on the logarithmic solution of the flux diffusion equation.