Investigation of magnetic flux trapping in high-T/sub c/ thin films by scanning SQUID microscope

The behavior of flux trapping in NdBa/sub 2/Cu/sub 3/O/sub y/ thin-film patterns with moats surrounding a 160 /spl mu/m square area has been investigated by a scanning superconducting quantum interference device (SQUID) microscope. Magnetic images were taken for moat patterns with three types of configuration and different size after cooling below T/sub c/ in various fields, and the threshold field for complete flux expulsion from the moat-surrounded area was estimated. It was found that the threshold field strongly depends on the size and gap of moats as well as their configuration. The largest enhancement of the threshold field by a factor of approximately seven as compared with that for an isolated square pattern was observed for the continuous moat pattern with broken corners.