Magneto-Optical and HREM Studies of Flux Pinning at Grain Boundaries in the bc Plane of Bi2212 Crystal

Abstract

Using a magneto-optical flux observation method, we have studied the flux pinning behavior of Bi2212 multi-crystalline samples. We find that flux pinning occurs at the intersections of small angle grain boundaries in Bi2212 multi-crystals when the magnetic fields are applied parallel to the ab plane. We can explain the flux density distribution by considering both the small-angle grain boundaries and intrinsic pinning effects. HREM observations show the existence of columnar defects such as misfit dislocations, distorted structure, and amorphous patches that run in approximately straight lines along the grain boundary. Such columnar defects, such as amorphous patches at the small angle grain boundaries, may be the origin of the flux pinning centers.