INVESTIGATION OF THE MAGNETIC-FLUX DENSITY DISTRIBUTION, CURRENT DISTRIBUTION AND MAGNETIZATION CURVE OF Y-BA-CU-O THIN-FILMS

In high quality Y1Ba2Cu3O7-x thin films with circular, triangular and quadratic shape, the magnetic flux density distribution (MFDD) and mag netization curve are measured. Comparison of calculated and measured M FDD shows good agreement and yields the critical current densities of the films. These j(c)-values agree with the j(c)-values calculated fro m the maximum magnetization which is reached at the external field mu( 0)H(p)'. Within the Bean model the field mu(0)H(p)' should agree with the penetration field mu(0)H(p) necessary for full flux penetration. T he measurements show that mu(0)H(p)' is smaller than mu(0)H(p) by a fa ctor of about 2. This is understood by taking into account a field dep endent critical current density. Furtheron a formula is presented for the magnetic stray-held in the center of a regular polygon with homoge neous thickness which gives also the penetration field mu(0)H(p).