Magneto-Optical Observation of Flux Density Distribution in YBa2Cu3O7-δ Bicrystal Films

The field dependences of inter-grain critical current density J c GB in YBa2Cu3O7-δ bicrystal films with [001] tilt grain boundaries (GBs) have been measured by the magneto-optical imaging technique. The results on the intra-grain critical current density J c IG were consistent with those obtained by the transport measurements. It was found that a bicrystal film with 4° tilt angle has a peak around 500 Oe in J c GB / J c IG -H curve, while the higher tilt angle films such as 24° have no peak in the curves. It seems possible to explain the peak in J c GB / J c IG -H curve by the matching field effect caused by the vortex pinning on the dislocation core array along the GB observed by TEM.