HIGH CRITICAL CURRENT DENSITY IN NEUTRON-IRRADIATED BULK YBa₂Cu₃O₇

Bulk melt-textured YBa 2 Cu 3 O 7 irradiated by fast neutrons has been investigated. We observed: (1) a critical current density (J c ) determined magnetically at 77 K exceeds 5×10 5 A/cm 2 in 0.1 T, 2×10 5 A/cm 2 in 1 T, and 1.2×10 3 A/cm 2 in 5.0 T; (2) at 5 K, J c is >2.1×10 7 A/cm 2 in 0.5 T, ~1.8×10 7 A/cm 2 at 1 T and >8×10 6 A/cm 2 in 5.0 T and (3) the J c -anisotropy decreases rapidly with the external field (H), e.g. at 77 K, it becomes 1 at ~4.8 T with J c ~3×10 3 A/cm 2 . We also found that (1) such a J c -enhancement is most effective in low H but less so in high H, (2) the enhancement is temperature independent at low H, (3) the pinning potential remains unchanged to within ~10% as J c varies by a factor of 15, and (4) thermal annealing up to 600°C recovers the un-irradiated state. These results and their implications are presented and discussed.