Effect of matrix composition on the flux pinning in a (Nd, Eu, Gd)Ba₂Cu₃O_y superconductor

In order to study the effect of matrix composition on flux pinning in the (Nd, Eu, Gd)Ba₂Cu₃O_y (NEG-123) bulk superconductors, we prepared two groups of samples with various rare-earth (RE) ratios using the oxygen-controlled-melt-growth (OCMG) process. For the first group, we kept the Nd content constant and varied the Eu/Gd ratio, and for the second group the Gd content was kept constant and the Nd/Eu ratio was varied. All the samples exhibited strongly developed fishtail effects and high critical current densities. Magnetization measurements revealed that the irreversibility field and the peak position systematically varied with Nd and Gd content. Scaling analyses suggested that two different pinning mechanisms are active in the NEG-123 system depending on the RE ratio. Those are ΔT_c pinning and normal-type pinning, however, we found that field-induced pinning also behaves like normal-type pinning on scaling analyses when ΔT_c is large. In conclusion, a difference in the peak position on scaled curves can be explained in terms of a difference in ΔT_c of field-induced pinning centers.