Superconducting properties of (Nd, Eu, Gd)-123

In the aim of optimizing the matrix composition to improve the critical current density (J_c) and to strengthen the flux pinning in the (Nd_0.33Eu_0.33Gd_0.33) Ba₂Cu₃O_y (NEG) bulk superconductors, we prepared two groups of NEG samples using a oxygen controlled melt growth process. For the first group we kept the Nd content constant and varied the Eu and Gd ratio, and for the second group the Gd content was kept constant and the Nd and Eu content was varied. In both cases we found a strongly developed fishtail effect and high critical current densities. Magnetization measurements revealed that, the irreversibility field and the peak position systematically varied with Nd content. However it was not systematic for Gd. The sample with Gd = 0.58 exhibited a large critical current density (J_c) of 90000 A cm^-2 at 77 K and 1.7 T.