Effect of interface pinning on dissipation, volume pinning force and measurement of upper critical magnetic field in MgB2 thin films

Angular dependences of resistivity (p) and critical current density (J(c)) have been measured to determine the effect of pinning at film-substrate and film-air interfaces on dissipation and volume pinning force in c-axis oriented MgB2 thin films prepared by the ex situ laser ablation technique. It is seen that for the field applied parallel to the ab-plane, interface pinning may reduce resistivity by two orders of magnitude while making nearly same contribution to total pinning force as pinning in bulk of the film. Angular dependence of the upper critical magnetic field (H,2) has been measured and it shows deviations from the anisotropic Ginzburg-Landau model. These deviations have also been understood in terms of the interface pinning effect. The results show that controlled addition of impurities and defects may significantly improve critical current densities in MgB2 superconductor. (C) 2002 Elsevier Science B.V. All rights reserved.