LOW-FIELD BEHAVIOR OF MAGNETIC AND TRANSPORT-PROPERTIES OF LASER-IRRADIATED ND-BA-CU-0 CERAMIC SUPERCONDUCTORS

Abstract

The low-field behavior of magnetic and transport properties of high-power laser-irradiated (Q-switched ruby laser, 694 nm, 30 ns) Nd-Ba-Cu-O (NBCO) ceramic superconductors prepared by the coprecipitation technique have been investigated. Laser-irradiated NBCO samples contribute significantly to the flux pinning for low applied magnetic fields. A well-defined field value H'c was observed for different laser-irradiated samples which is characteristic of a cross-over between regions dominated by the inter- and intragranular effects. The value of H'c for a laser-irradiated sample is increased with increasing number of laser pulses. Thermal modeling of laser heating reveals that on irradiation the surface melts up to a depth of 1 mum and laser-induced evaporation occurs at energy density 2.5 J/cm2. SEM studies showed grain growth due to laser-induced surface sintering which improves the interconnectivity among the superconducting grain structure and thus attributed to physical densification and consequent reduction in the total number of weak links. The increase of flux trapping and transport critical current density after laser irradiation is determined by the rigidity of the flux line lattice which may be due to the presence of additional pinning centers caused by the creation of laser-induced mobile defects and their clusters.