Investigation of the magnetic flux density distribution, current distribution and magnetization curve of YBaCuO thin films

Abstract

In high quality Y 1Ba 2Cu 3O 7− x thin films with circular, triangular and quadratic shape, the magnetic flux density distribution (MFDD) and magnetization curve are measured. Comparison of calculated and measured MFDD shows good agreement and yields the critical current densities of the films. These j c -values agree with the j c -values calculated from the maximum magnetization which is reached at the external field μ 0 H′ P. Within the Bean model the field μ 0 H′ P should agree with the penetration field μ 0 H P necessary for full flux penetration. The measurements show that μ 0 H′ P is smaller than μ 0 H P by a factor of about 2. This is understood by taking into account a field dependent critical current density. Furtheron a formula is presented for the magnetic stray-field in the center of a regular polygon with homogeneous thickness which gives also the penetration field μ 0 H P.