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

We have used an AC transport technique to measure the force-displacement response of vortices in granular NbTa thin films. Results are presented for the dependence of this behaviour as the applied magnetic field amplitude and its orientation with respect to the columnar microstructure is varied. Analysis of the results allows us to determine the effective gradient of the pinning wells and elastic limit of the displacement of the vortices before depinning. The pinning site density, distribution and strengths are also deduced. The results are seen to correlate well both with the DC transport properties and with independent microstructural investigation of the thin film samples. They are analysed using various theoretical predictions and also compared to similar measurements recently reported on YBCO films.