CURRENT AND FIELD DISTRIBUTIONS IN SUPERCONDUCTING FILMS - DETERMINATION OF CRITICAL-CURRENT BY LOCAL-FIELD MEASUREMENT

The current J and magnetic field H distributions in a thin film have been calculated for arbitrary changes of the external field (H(e)). A joint solution of equations describing the field and current distributions in three different states (Meissner, critical and mixed) taking into account a tangential field has been found. The decrease of the external field leads to the appearance of the mixed state with a current less than the critical one (J < J(c)). A simple method for deriving the function J(c)(H) from the experimental dependence H(p)(H(e)) (H(p) = the normal field in the centre of the film) has been suggested. An example given for a thin ceramic disk shows good agreement of magnetic and transport J(c) values at H(e) = 0. The hysteresis loops H(p)(H(e)) calculated on the basis of the functions J(c)(H) found for a ceramic disk and a thin film fitted well with the experimental data.