CORRELATION OF PINNING PROPERTIES WITH SUPERCONDUCTING AND MICROSTRUCTURAL PARAMETERS IN NBTA THIN-FILMS

We have used an AC transport technique to measure the force-displaceme nt response of vortices in granular NbTa thin films. Results are prese nted for the dependence of this behaviour as the applied magnetic fiel d amplitude and its orientation with respect to the columnar microstru cture is varied. Analysis of the results allows us to determine the ef fective gradient of the pinning wells and elastic limit of the displac ement of the vortices before depinning. The pinning site density, dist ribution and strengths are also deduced. The results are seen to corre late well both with the DC transport properties and with independent m icrostructural investigation of the thin film samples. They are analys ed using various theoretical predictions and also compared to similar measurements recently reported on YBCO films.