Vortex pinning and twin boundaries in YBa2Cu3O7−δ thin films

Abstract

The interaction between magnetic flux vortices and twin boundaries is investigated in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ thin films. Films grown to various thicknesses, and cooled along different paths in the ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ phase diagram, are shown to have various twin boundary microstructures and densities. It is demonstrated that changes in processing result in differences in the vortex-pinning behavior of the films, but that these differences are not due to changes in the microstructure of the twin boundaries. Further, observed differences in the twin spacing do not result in changes in the volume pinning force. This is found to be true in the magnetic-field regime spanning the range from where the flux vortex spacing is large relative to the twin density to where the vortex spacing is small relative to this density.