We have measured the pinning force due to twin boundaries by measuring the magnetic torque produced when a field is applied perpendicular to the c axis and rotated with respect to the ab axes. At 76 K, the torque increases roughly fourfold, when the field is within 2°of the parallel to the twin boundaries. This peak is absent at 27 K. Irradiation with 5×101 6 cm-2 3.5 MeV protons increases the overall critical current and eliminates the peaks observed at 76 K.
|Number of pages||3|
|Journal||Applied Physics Letters|
|State||Published - 1 Dec 1990|