Flux pinning properties of (Nd,Eu,Gd)Ba₂Cu₃O _y (NEG-123) superconductor with 211 phase particles

Flux pinning properties were investigated by focusing on the origin of the high peak critical current density and the high irreversibility field for Nd_0.33Eu_0.38Gd_0.28Ba₂Cu ₃O_y (NEG-123) bulk superconductors with the addition of 211 secondary phase particles of volume fractions up to 10mol%. It was found that a negative correlation exists between the peak critical current density J_cp and the irreversibility field B_i for various fractions of added 211 phase. This suggests that the mechanisms that determine J _cp and B_i are different. The 211 particles do not contribute to the peak effect neither directly through the pinning mechanisms of the condensation energy interaction nor indirectly with the aid of the order-disorder transition of flux lines. Other possible defects are nano-lamella structures. Although these defects do not directly contribute to the peak effect through the pinning mechanism of the condensation energy interaction, they may contribute to it with the aid of the order-disorder transition of flux lines. On the other hand, as B_i deteriorates with the addition of 211 particles, it is not determined by the flux pinning of 211 particles. The decrease in B_i is considered to be caused by the proximity effect of nano-lamella structures.