Effects of artificial structures of defects on the magnetic response of superconducting films: first penetrations; thermoremanence; computational simulations and granularity

Abstract

In a recent work we have investigated some structured superconducting systems for which a number of noticeable characteristics have been verified, such as the saturation of the remanent magnetization for fields above the first matching field; layer-by-layer vortex penetration at low temperatures and vortex densities (low excitation fields). Understanding all details of such a behavior is essential for a deeper comprehension of the possible varieties of vortex-antidot interactions and, although being an essentially fundamental study, its implications go much beyond, extending to aplications, in view of the crucial role played by those interactions on the limitations of the critical current. Trapped flux can exhibit a variety of states, what has direct impact on the performance of prospective devices based on magnetization and its time-evolution. The grouop hosting this work has a large experience on the study of granular superconductors, so that the possibililty of a complete control of sample granularity opens up a new road leading to an ample comprehension about the whole variety of ways of trapping magnetic flux in such materials. Samples employed during the development of this project will be superconducting films of several materials (Nb, Pb, MgB2 and YBCO) in which arrays of defects will be inserted, with characteristics specific for each study. The arrays will be prepared with different periodicities as well as different frame widths of intact material around the antidots. We will use AC and DC magnetometry, electrical transport,magento-optical imaging and Hall microprobing. Specifically for the study with granular superconductors, the antidots will be inserted to form grain boundaries, so as to control parameters such as grain sizes and densities.