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Visit of Prof. Alejandro V. Silhanek to the laboratories of GSM-DF/UFSCar


Prof. Silhanek has a large experience studying the magnetic response of superconducting films decorated with structures of defects (antidots, ADs). Throughout the years he has actively participated of successful studies on structured Pb films. A practical difficulty with those films is their fast degradation, even when kept in inert atmosphere environments. Since about one year we have conducted, at GSM, experiments with samples prepared in Leuven by Prof. Silhanek. These are novel studies about the harmonic content of the susceptibility in superconducting films with networks of ADs. Immediately after preliminary investigations, it became clear that this new approach which we have proposed has a great potential to be explored, but the samples could not be reexamined simply because of the considerable degree of degradation after only two months since fabrication. It was necessary to produce new samples to continue the study. Thus we proposed a material substitution, indicating Nb which, at first contact with air, forms a passivating Nb-oxide layer, that eliminates the problem associated with the progressive degradation presented by Pb. The Leuven group tried - unsuccessfully - to fabricate structured films of Nb. Since we have a fruitful collaboration with Prof. Mark Blamire´s group (Cambridge), which has provided us with excellent Nb films, we managed to initiate, under our coordination, a triangular partnership in which the Leuven group used its previous experience to produce adequate substrates, with columns that are removed "a posteriori". Those substrates were then sent to Cambridge, for a variety of deposition tests with Nb. After a few trials, followed by adjustments on the deposition parameters, a batch of films with AD structures was obtained, after the successful remotion of the columns, and then studied in terms of microstructure morphology. Those Nb structured films just arrived in our laboratory and were tested regarding magnetic response, with quite promising results. During Prof. Silhanek´s visit we intend to analyze and discuss in great detail the results of the experiments that will be conducted in the coming couple of months with the new samples, aiming at a fast publication of one or more scientific papers based on the execution of such doubly innovative strategy: harmonic susceptibility studies (novel in structured films) with Nb samples having networks of ADs (probably unique in the world).While with us, Prof. Silhanek will teach a 10-hour minicourse (graduate level) about Nanostructured Superconductors. He will also attend the XXXIII Condensed Matter Physics National Meeting (Águas de Lindoia, May 10 to 15, 2010), delivering two presentations: "Direct visualization of the vortex statics and dynamics via scanning Hall microcopy" at the Symposium "Superconductivity and Magnetism in Strongly Correlated Systems"; and "Local probing of the vortex-antivortex dynamics in superconductor/ferromagnet hybrid structures", at one of the Oral Sessions of the Thematic Group "Superconductivity and Strongly Correlated Systems". (AU)

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