Flux Pinning Properties at High Temperatures in (Nd, Eu, Gd)Ba2Cu3Oy Superconductors with 211 Secondary Phase Particles

Abstract

Critical current density, Jc, and irreversibility field, Bi, were measured in a magnetic field along the c-axis for (Nd, Eu, Gd)Ba2Cu3Oy (NEG-123) bulk superconductors with the addition of Rare Earth (RE)-211 phase particles in order to correctly understand the flux-pinning mechanism in these superconductors. It was found that the peak value of the critical current density, Jcp, increased and that Bi tends to decrease with the addition of 211 phase particles. That is, a negative correlation exists between Jcp and Bi. The deterioration of Bi is mainly attributed to the deterioration of the upper critical field, Bc2, caused by the proximity effect between substituted regions with lower Bc2 and the surrounding 123 matrix. The peak effect is caused by the order-disorder transition of the flux lines with the assistance of pinning by the nano-lamellas. The observed results can be explained well by the theoretical predictions of the flux creep-flow model.