MAGNETIC AND TRANSPORT CRITICAL-CURRENT DENSITY OF LASER-IRRADIATED SM-BA-CU-O SUPERCONDUCTOR AT 4.2-K

Abstract

The low temperature (4.2 K) magnetic and transport critical current density of laser-irradiated (Q-switched ruby laser, 694 nm, 30 ns) Sm-Ba-Cu-O ceramic superconductors prepared by the coprecipitation technique have been investigated. Laser irradiation did not significantly change the structural parameter and the critical transition temperature T(c) but caused an appreciable increase in magnetic critical current density J(mc) and transport critical current density J(tc). Inverse a.c. Josephson effect studies at 77 K showed a sharp decrease of microwave-induced d.c. voltage after laser irradiation. SEM studies revealed partial melting at grain boundaries and grain growth due to sintering which improves the interconnectivity in the network of superconducting grain structures after laser irradiation. These phenomenon are attributed to physical densification and consequent reduction in the total number of weak links between the superconducting grains. The significant increase of J(mc) and J(tc) after laser irradiation is presumably connected with the creation of irradiation-induced mobile defects which act as pinning centers and, bence, stronger Josephson current paths between the superconducting intergrains.