The collective flux pinning force in (Sm0.5Eu0.5)Ba2Cu3O7-delta superconductors

摘要

We have measured the isothermal magnetization loops of top-seeded melt processed (Sm0.5Eu0.5) Ba2Cu3O7-delta + 10 mol% (SmEu) BaCuO5 + 10 wt% Ag crystals in a magnetic field up to 8 T parallel to the c-axis from 50 to 87 K using a vibrating sample magnetometer. All of the isothermal J(c)(H) curves show a second peak. The scaling of the F-p - H curves indicates that the flux pinning force F-p comes from the collective pinning of two kinds of pinning centres, F-p = F-p(H) + F-p(L). One (F-p(H)) is the Delta T-c-type pinning centre originating from the RE - Ba and RE - RE substitution responsible for the second peak; the other (F-p(L)) is the normal pinning contributed by the surface and point pins. The H-c2 - T diagram implies two critical temperatures. The crossover occurs at about 88.2 K.