Flux Pinning Properties at High Temperatures in (Nd, Eu, Gd)Ba₂Cu₃O_y Superconductors with 211 Secondary Phase Particles

Abstract

Critical current density, J_c, and irreversibility field, B_i, were measured in a magnetic field along the c-axis for (Nd, Eu, Gd)Ba₂Cu₃O_y (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, J_cp, increased and that B_i tends to decrease with the addition of 211 phase particles. That is, a negative correlation exists between J_cp and B_i. The deterioration of B_i is mainly attributed to the deterioration of the upper critical field, B_c2, caused by the proximity effect between substituted regions with lower B_c2 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.