Magneto-Optical Investigation of the Critical State in Coated Conductors: Peculiarities of the Magnetic Field Distribution and the Determination of the Critical Current Density

In this paper, we present a detailed analysis of the results of the magneto-optical measurements of the field's topography in the coated conductor (CC) tapes at various temperatures in order to study the distribution of the field and develop a simple method for determining the critical current density. It is shown that the fitting of calculated field profiles to the results of the magneto-optical measurements gives a satisfactory agreement between the model and the experiment. In addition, we proposed a method for the determination of the critical current density from measurements of the topography of the transverse field that is insensitive to the precise form of the current lines. Furthermore, it is shown that the experimentally observed asymmetry of the field profile is probably due to a slight misalignment between the MOI film and the CC tape, which is possibly due to the presence of a small transverse curvature of actual CC tapes.