Self-organized current transport through low angle grain boundaries in YBa2_2Cu3_3O7−δ_{7-\delta} thin films, studied magnetometrically

The critical current density flowing across low angle grain boundaries in YBa$_2$Cu$_3$O$_{7-\delta}$ thin films has been studied magnetometrically. Films (200 nm thickness) were deposited on 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 - 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.Comment: 8 pages, including 7 figure