Investigation of magnetic flux trapping in high-T-c thin films by scanningSQUID microscope

The behavior of flux trapping in NdBa2Cu3Oy thin-film patterns with moats s urrounding a 160 mum square area has been investigated by a scanning superc onducting quantum interference device (SQUID) microscope. Magnetic images w ere taken for moat patterns with three types of configuration and different size after cooling below T, in various fields, and the threshold field for complete flux expulsion from tile moat-surrounded area was estimated. It w as found that the threshold field strongly depends on the size and gap of m oats as well as their configuration. The largest enhancement of the thresho ld field by a factor of approximately seven as compared with that for an is olated square pattern was observed for the continuous moat pattern with bro ken corners.