MAGNETIC-RELAXATION OF INTERGRANULAR CRITICAL-STATE IN SINTERED YBA2CU3O7-DELTA

The relaxation of the zero-field-cooled magnetisation of three sintere d samples of YBa2Cu3O7-delta has been measured at low fields. Special attention was paid to the low-field regime where the motion of intergr anular vortices is dominating the decay of the magnetisation. From the measured data the apparent activation energy for flux jumps, U0, was calculated. The extracted values fall in the range 0.6-2 eV, considera bly higher than what has been found for the intragranular flux creep b ut in the same range as reported by others for intergranular creep. Th e samples showed somewhat different behaviours and the sample with the most homogeneous morphology had the lowest value of U0. This can be e xplained within theories for pinning in granular superconductors.