Sharp angular sensitivity of pinning due to twin boundaries in Ba2YCu3O7

Abstract

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 5×1016 cm−2 3.5 MeV protons increases the overall critical current and eliminates the peaks observed at 76 K.