High critical current density and its field dependence in mixed rare earth (Nd,Eu,Gd)Ba_2Cu_30_(7-δ)thin films

摘要

Compared with mono-rare earth 123 films, ternary rare earth (Nd,Eu,Gd)Ba_2Cu_30_(7-δ) (NEG123) films show higher critical current density (J_c) and improved irreversibility field (H_(irr)), but no increase in the characteristic field corresponding to a crossover from a low-field plateau to a linear region in a log J_c-log H plot. At intermediate fields, J_c vs H scales as H~((-0.5±0.05)) for NEG123, in contrast to H~((-0.73±0.05)) for mono-rare earth samples such as Gd123. The slow power decay of J_c vs H together with the improved J_c and H_(irr) strongly implies that extra flux pinning centers exist in NEG123, which are thought to be noncorrelated stress fields induced by lattice mismatch.