MAGNETIC-FLUX MAPPING, MAGNETIZATION, AND CURRENT DISTRIBUTIONS OF YBA2CU3O7 THIN-FILMS BY SCANNING HALL PROBE MEASUREMENTS

Mapping of the magnetic flux distribution in a square-shaped supercond ucting YBa2Cu3O7 thin film was carried out using a scanning micro-Hall probe with a spatial resolution of about 25 mum. Calculation procedur es for converting the measured flux map to the film current distributi on are discussed. The flux penetration with the applied field perpendi cular to the film surface was studied in initially zero-field-cooled s amples. With full flux penetration, the film sheet currents follow the sample edges, whereas with partial flux penetration, the sheet curren ts are more complex and include multiply connected patterns. In both c ases the sheet currents change their flow direction abruptly along the sample diagonals where the shielding is more effective, and this resu lts in distinctive minima of the flux penetration. The saturation magn etization for a square-shaped sample of side 2a was found to be identi cal to that for disc and cylindrical samples of radius a. It is shown that the multiply connected current patterns corresponding to various parts of the hysteresis cycle can be reconstructed from the superposit ion of two appropriate virgin current distributions. The critical curr ent density was dependent on magnetic flux density, and it was found t o follow the Kim model.