Structure of the mixed state induced in thin YBaCuO superconducting films by the field of a small ferromagnetic particle

The temperature dependence of the local energy barrier to formation of the mixed state in YBaCuO thin-film superconducting samples has been determined . The measurement technique is based on use of a small ferromagnetic partic le as the magnetic field source. It is found that the energy barrier to cre ation of vortices (for the field oriented parallel to the CuO planes) is an omalously small while the dependence of the corresponding threshold current j(c)(T) differs substantially from the temperature dependence of the pair- breaking current. The experimental results are interpreted in terms of the model of a Josephson medium. The observed temperature dependence of j(c) po ints to a strong suppression of the superconducting order parameter at the intergrain boundaries, which for the most probable type of boundaries: supe rconductor-insulator-superconductor, is evidence of anisotropic pairing. (C ) 1999 American Institute of Physics. [S1063-7761(99)01711-4].