QUANTITATIVE MAGNETO-OPTICAL ANALYSIS OF SUPERCONDUCTORS

Abstract

A magneto-optical equipment has been set up and carefully calibrated. In this paper, we shortly review the main characteristic of this equipment, then we focus on the analysis to be performed in order to extract from magneto-optical images the local values of magnetic induction and electrical current density along the superconducting sample. This implies the numerical inversion of the Biot-Savart law. A detailed analysis modeling the interaction of the spontaneous magnetization across the indicator film with the magnetic fields in the specimen region has been performed. In particular, we take into account the generally disregarded interaction of the indicator film with in-plane magnetic fields, i.e. with the component parallel to the indicator surface. A set of experimental data on YBCO films is presents to show the actual impact of the new analysis method, for what concerns both the local values of the magnetic induction and the electrical current density evaluation. A critical comparison of the new obtained data with known electrodynamical models in made. It results that, in the Meissner state, a simple electrodynamical model nicely describes the electrical current obtained from our experimental data. On the contrary, in the critical state, the Bean model does not account well for the observel local variations of the critical current along the sample.