Magneto-optical investigation of flux penetration in Y1Ba2Cu3O7 thin films

Using the magneto-optical Faraday effect the magnetic flux penetration into high Tc superconducting Y1Ba2Cu3O7 thin films is investigated. Epitaxially grown high quality films (Tc≳88 K, jc≳106 A/cm2 at 77 K) show a flux penetration in three steps, the formation of a flux front if the acting magnetic field reaches Hc1 at the edge of the specimen, the movement of the flux front towards the center of the sample, and the increase of the flux density after the flux front reaches the center. The remanent state shows trapped magnetic flux in the film, indicating inhomogeneously distributed pinning centers.