Matrix chemical ratio and its optimization for highest flux pinning in ternary (Nd-Eu-Gd)Ba₂Cu₃O_y

We have fabricated the ternary (Nd, Eu, Gd)Ba₂Cu₃O_y system with various Nd:Eu:Gd ratios with the aim of optimizing the pinning performance at 77 K. The magnetization measurements suggest that the three elements (Nd, Eu, Gd) contribute to pinning in different manners: Nd mainly enhances flux pinning at low magnetic fields, Eu controls the second peak position and the irreversibility field, while Gd slightly enhances intermediate and high-field J_c values. The scaling analysis of the pinning force density versus the reduced field h = H_a/H_irr showed a peak at h = 0.55. This value is higher than the theoretically predicted highest value of h = 0.5, corresponding to ΔT_c pinning. We proved that an excellent flux pinning can be achieved in the entire magnetic field range when sub-micron secondary phase particles are dispersed in the NEG-123 matrix with an optimum Nd:Eu:Gd ratio.