Effect of Eu/Gd ratio on flux pinning in (Nd, Eu, Gd)-Ba-Cu-O

We have studied the magnetic properties of (Nd_0.33Eu_xGd_(0.66-x))Ba₂Cu₃O_y bulk samples prepared by the oxygen-controlled melt-growth (OCMG) process, in which x ranged from 0 to 0.33. The heat treatment profiles for melt processing were determined according to the peritectic decomposition temperatures obtained from thermal analysis measurements. X-ray diffraction confirmed that the main phase is NEG-123 and the unit cell size decreases monotonously with increasing Gd content in the NEG-123 matrix, supporting the presence of a complete Nd-Eu-Gd solid solution. The sample with x = 0.08 exhibited a large critical current density (J_c) of 90 000 A cm^-2 at 77 K and 1.7 T for H∥c-axis. The scaling analyses of the volume pinning force showed that the peak position in the scaling curve was dependent on the Eu/Gd ratio, which indicates that the matrix composition mainly controls the ΔT_c-pinning mechanism.