Critical current hysteresis in low angle Y-Ba-Cu-O bicrystals

We study the transport critical current of c-axis YBCO films grown on low angle [001] tilt bicrystals of 2.5°, 5°, and 7.5°. The influence of low magnetic fields on each single grain boundary has been studied at different temperatures by varying the field direction in the plane of the boundary with the magnetic field always perpendicular to the bias current. The tilt angle, θ, between the magnetic field direction and the normal to the film surface has been varied from -110° to +110°, where 0° corresponds to the field direction parallel to the c-axis of the film. We find that the angular dependence of the critical current density Jc shows a hysteretic behavior for applied magnetic fields below 1T. Maxima of Jc are observed at different angles depending on the rotation direction of the applied magnetic field. We notice that the angular difference between the critical current peaks is a function of the external magnetic field, so that for strong fields only the ±90° maxima are observed. We relate these observations to the intrinsic pinning between CuO layers, and to trapped flux in the superconducting film.