MAGNETIC-FLUX PENETRATION AND CURRENT-DENSITY IN SUPERCONDUCTING THIN-FILMS

The magnetic behaviour of type-II superconducting thin films subjected to a transverse external field can be explained taking demagnetising effects into account, We studied this problem following two different approaches: on the one hand, we computed flux diffusion and circulatin g currents, on the basis of a recent model presented in the literature ; on the other hand, we carried out measurements of local magnetic fie ld on the film surface by means of a self-made Hall probe magnetometer , We compared the measured and the computed hysteresis loops and magne tisation decays and we found good agreement. By the fit of the experim ental hysteresis loops, we also obtained the dependence of the critica l current density on temperature and local magnetic field in YBCO thin films. (C) 1998 Elsevier Science B.V.