Angular effects of the critical current in Nb/Pd multilayers

Abstract

The angular dependencies of the critical current density, Jc⵼⵼⵼, for superconducting Nb/Pd multilayers which show, in parallel magnetic field, a pronounced peak effect, were investigated ⵼here ⵼ is defined as the angle from the plane parallel to the sample surface⵼. We have demonstrated that the procedure of measurements is an important factor for the Jc⵼⵼⵼ shape. When rotating the sample in a fixed magnetic field H, it was found that the external field direction at which the maximum of Jc was obtained form an angle different from zero with respect to the planar direction. The angular position of the maximum depends on the external magnetic field, as well as on the initial conditions under which the samples were kept. It is found that the more intense the peak effect is on the Jc⵼H⵼ curves, the larger the angular shift is of Jc⵼⵼⵼ in these structures. The results are explained in terms of the magnetic field suppression of the percolation currents in a weak-link network. Flux trapped within grains by the flux pinning processes is relatively stable at low fields and its contributions to the transport current suppression add vectorially to the applied field.