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

The low-field behavior of magnetic and transport properties of high-po wer laser-irradiated (Q-switched ruby laser, 694 nm, 30 ns) Nd-Ba-Cu-O (NBCO) ceramic superconductors prepared by the coprecipitation techni que have been investigated. Laser-irradiated NBCO samples contribute s ignificantly to the flux pinning for low applied magnetic fields. A we ll-defined field value H'c was observed for different laser-irradiated samples which is characteristic of a cross-over between regions domin ated by the inter- and intragranular effects. The value of H'c for a l aser-irradiated sample is increased with increasing number of laser pu lses. Thermal modeling of laser heating reveals that on irradiation th e surface melts up to a depth of 1 mum and laser-induced evaporation o ccurs at energy density 2.5 J/cm2. SEM studies showed grain growth due to laser-induced surface sintering which improves the interconnectivi ty among the superconducting grain structure and thus attributed to ph ysical densification and consequent reduction in the total number of w eak links. The increase of flux trapping and transport critical curren t density after laser irradiation is determined by the rigidity of the flux line lattice which may be due to the presence of additional pinn ing centers caused by the creation of laser-induced mobile defects and their clusters.