Vortex dynamics of 250 MeV Ag ions irradiated YBCO films

YBCO thin films with c-axis orientation were grown in-situ by KrF laser on LaAIO(3) substrate. The films were irradiated with 250 MeV Ag ions at doses equivalent to B-phi ranging from 1 T to 4 T. Critical currents were measur ed using SQUID magnetometer with field parallel to columnar defects. There is a marked enhancement of vortice pinning due to generation of additional pinning centres. There seems to be an upper limit to the irradiation doses beyond which there is a 'smearing effect' on J(c). We also find a shift in Irreversibility Line towards higher field which is attributed to better pin ning induced by columnar defects. Defect production is examined in the fram ework of "Coulomb explosion" model and the consequences are analysed in ter ms of defect-induced behaviour within the purview of models such as "Bean m odel",'Exponential model' and "Vortex Glass" model. We point out that the ' stress model' provides a qualitative explanation for the reduced T-c and a broad transition at high fluence. (C) 1999 Elsevier Science B.V. All rights reserved.