Determination of the Critical Current in High-T_c Superconducting Thin Films by a Magneto-Optical Method

Abstract

Normal flux density gradient along the film plane in TmBa₂Cu₃O_7-x superconducting thin films have been measured by a magneto-optical method using magnetic garnet films covering the superconducting sample as a sensor of magnetic field. Critical current density J_c was determined by means of standard four-probe technique for the same samples. A comparison between J_c and the value of the normal flux density gradient suggests that the critical current is sustained primarily by the normal gradient in the in-plane component of flux density. It means that a conventional analysis ignoring the flux-line curvature can not be aplied to the superconducting thin films.