Angular dependent flux pinning studies of superconducting layered structures

Angular dependences of the critical current density (J/sub c/(/spl theta/)) in superconducting multilayers based on Nb/NbO/sub x/ were investigated in this work. In rotating of the sample at a fixed magnetic field, it,vas found that the direction of the external field at which the maximum of J/sub c/(/spl theta/) was obtained formed an angle with the planar direction. The rotation leads to the existence of the kink structure even in a magnetic field parallel to the layers. This results from the difficulties of the transition of the flux vortex lattice into the ground state with minimum energy. In accordance with the model, bringing of the lattice into the ground state before every measurement at a new angle results in the symmetrical angular dependence of the critical current.