ANISOTROPIC ENHANCEMENT OF THE CRITICAL CURRENT-DENSITY OF EPITAXIAL YBA2CU3O7-X FILMS BY FAST-NEUTRON IRRADIATION

High-quality epitaxial thin films of YBa2Cu3O7-x were irradiated with fast neutrons (E > 0.1 MeV) up to fluences of 2×1018 cm-2. The critical transport current density jc (resistively measured) initially was about 2×107 A/cm2 at 4.2 K and increased after a fluence of 4.9×1017 cm-2 even in vanishing magnetic fields by 50%, and in magnetic fields of up to 8 T by 300%. The enhancement was measured at angles of 0°, 30°, 60° and 90° between the c-axis of YBa2Cu3O7-x and the B-vector, being the greatest at B∥c, for which direction also a slower decrease of Tc(B) with increasing magnetic field was observed after irradiation than before. The increase of jc in vanishing magnetic fields after irradiation can be explained by enhanced pinning of the magnetic self-field of the critical current or an increase of Bc1. In magnetic fields, the increase of jc can be understood by the irradiation effects, which have already been studied in detail in a A15-superconductors. © 1990.