Magnetic field and current distributions at an artificial grain boundary in YBa2Cu3O7-x

Using a magneto-optical technique, magnetic field distributions have been m easured in melt-textured YBa2Cu3O7-x, joined to form an artificial grain bo undary, in an external magnetic field perpendicular to the sample surface. An inversion scheme using the inverse-matrix method has been applied to obt ain the current distribution from the magnetic field distribution. Both mag netic field and current distributions around the grain boundary show differ ent behaviour between the field increasing up to 150 mT and decreasing down to 0 T after zero-field cooling. The magnetic field at a weakly coupled se ction of the grain boundary in the increasing field is higher than that in the decreasing field, even in the same external field. This study supports a model in which such differences in the magnetic field at the weak-link gr ain boundaries give rise to the hysteresis behaviour in the field dependenc e of transport critical current density in polycrystalline samples.