THE QUANTITATIVE-DETERMINATION OF FLUX-DENSITY GRADIENTS AND VOLUME PINNING FORCES IN PATTERNED YBCO THIN-FILMS USING THE MAGNETOOPTICAL FARADAY-EFFECT

In circular patterned YBCO thin films the penetration of magnetic flux is observed directly and locally using the high resolution magneto-optical Faradayeffect in fields applied perpendicular to the film plane. The radial distribution of the z- component of magnetic flux B(z)(r) and its gradient partial derivative B(z)/partial derivative r are measured. For the determination of the critical current density mu-o(j)c = rotB the curvature of the radial component partial derivative B(r)/partial derivative z cannot be neglected, consequently, the determination of j(c) must be obtained by a comparison of measured and calculated B(z)(r) profiles. Values for j(c) determined by this procedure agree fairly well with the corresponding transport critical current as well as the magnetically determined j(c).