Significant differences in superconducting and microstructural properties between two types of MgB2 films prepared by pulsed laser deposition were determined. A very high Hc2-T slope of 1.1 T/K was achieved in the in situ film. The Jc-H curves of the in situ film also show a much weaker field dependence than that of the ex situ film. The magneto-optical (MO) images show that at 4 K the flux penetrates the in situ MgB2 film through random paths, while for the ex situ film, the flux penetration pattern is mostly repeatable, indicating a defect-controlled flux penetration. Microstructural study (transmission electron microscopy and atomic force microscopy) revealed a relatively big grain size in the ex situ film. The correlation between the superconducting properties, microstructure and preparation conditions is discussed with regard to the two types of films.
Available at: http://works.bepress.com/jhorvat/18/