SIMILAR SHIFTS OF THE DEPINNING AND IRREVERSIBILITY LINES BY OXYGEN IRRADIATION OF MELT-PROCESSED BI2SR2CACU2O8

With the vibrating reed technique and DC magnetization we have measured the depinning and irreversibility lines, the Labusch parameter and the dissipation caused by the flux line movement, before and after irradiation of a dense melt-processed Bi2Sr2CaCu2O8 superconductor. The sample was irradiated with 1.5x1015 cm-2 400 MeV oxygen ions. After irradiation, the shift of the depinning line to higher reduced temperatures measured with the vibrating reed is similar to the shift of the irreversibility line. This result and the changes observed in the Labusch parameter and damping of the reed indicated unambiguously an increase in the pinning strength after irradition. The observed changes provide evidence supporting the thermally activated depinning interpretation and the diffusion character of the flux motion. The estimated average activation barrier follows a field dependence close to B-0.25 for fields larger than ∼0.2 T. © 1990.