Study of flux behavior in Bi₂Sr₂CaCu₂O₈ single crystal in external magnetic fields up to 1 T

Using the high-resolution Faraday effect (HRF) technique, the behavior of magnetic flux in Bi₂Sr₂CaCu₂O₈ single crystals is visualized in external magnetic fields up to 1 T. This technique reveals defects in many of these crystals which are probably twin planes. X-ray measurements indicate that two adjacent crystallites have c-axis lattice vectors which deviate from each other by about one degree. As a consequence of these defects, the shielding currents break up in sub-loops, each shielding a defect-free part of the sample. This leads to an underestimate of the critical current values determined by non-local magnetization measurements. Magneto-optical images can be used to calculate the necessary correction.