Enhancement of critical current in melt processed Bi 2Sr 2CaCu 2O 8 by irradiation with 400 MeV oxygen ions

Abstract

Dense melt processed Bi 2S 2CaCu 2O 8 superconductor was irradiated below T c with 400 MeV oxygen ions up to a dose of 1.55 × 10 15 cm −2. Nearly linear with the dose we found a drop in T c of 7 K and an increase of resistivity of 37% which recovered partly during annealing at 300 K. Irradiation and annealing did not alter the transition width. After irradiation the irreversible magnetization showed a marked increase at low temperatures, while the adverse effect of T c reduction seemed to prevail for T > 60 K. On the other hand the logarithmic time decay 1/ M d M/d ln t was nearly unchanged. This indicates, that the irradiation induced defects act as additional pinning centers with an activation energy U close to that of the intrinsic defects. In contrast to magnetization currents, irradiation was found to enhance the critical transport current density j c ( B, T) mainly at higher temperatures. In particular the marked decrease of j c with field, which was found before irradiation, was reduced.