Flux-line interactions with precipitates in YBa2Cu3O7-x films revealed by scanning Hall probe microscopy

We have used scanning Hall probe microscopy to study the interaction betwee n flux lines and a random array of precipitates in thin YBCO films. Pinning by precipitates has been demonstrated by measuring the distribution and ma gnetic held profiles of individual flux lines. Flux lines in the film with precipitates have strongly preferred locations as well as a much broader ra nge of shapes and sizes compared to YBCO films without precipitates. We hav e also observed "local magnetization" anomalies, which appear at multiples of the matching field for the random array of pinning sites.