Self-organized current transport through low-angle grain boundaries in YBa 2 Cu 3 O 7 − δ thin films studied magnetometrically

The critical current density flowing across low angle grain boundaries in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ thin films has been studied magnetometrically. Films (200 nm thickness) were deposited on ${\mathrm{SrTiO}}_{3}$ bicrystal substrates containing a single [001] tilt boundary, with angles of 2, 3, 5, and 7 degrees, and the films were patterned into rings. Their magnetic moments were measured in applied magnetic fields up to 30 kOe at temperatures of 5\char21{}95 K; current densities of rings with or without grain boundaries were obtained from a modified critical state model. For rings containing 5 and 7 degree boundaries, the magnetic response depends strongly on the field history, which arises in large part from self-field effects acting on the grain boundary.