Magnetic imaging of high-T-c films with grain boundaries by a scanning SQUID microscope

The magnetic flux trapped or generated in high-T-c films with [001]-tilt gr ain boundaries has been observed directly by using a scanning superconducti ng quantum interference device microscope in a wide temperature range of 6- 90 K. In the measurements for a field-cooled NdBa2Cu3Oy sputtered thin film with a symmetric 36.8 degrees grain boundary, some of the flux quanta trap ped at the grain boundary were found to disappear or change their positions at high temperatures near T-c, clearly indicating weaker pinning strength at the boundary. For a Y-Ba2Cu3Oy LPE film with an asymmetric 45 degrees gr ain boundary, unquantized disordered flux was observed along the grain boun dary, of which magnitude was found much larger than that previously reporte d for PLD films. (C) 2001 Elsevier Science B.V. All rights reserved.