Optimization of matrix chemical ratio for high flux pinning in ternary (Nd-Eu-Gd)Ba2Cu3Oy

We prepared (Nd, Eu, Gd)Ba2Cu3Oy samples with various Nd: Eu: Gd ratios in the rare earth site. It was found that the three elements contributed to fl ux pinning in different ways. Nd mainly enhanced flux pinning at low magnet ic fields, Eu controlled the second peak position and the irreversibility f ield, while Gd slightly enhanced intermediate and high-field J(c) values. S caling analyses for the pinning force density as a function of the reduced field h=H-a/H-irr (where H-irr denote the irreversibility field) showed tha t the highest peak was achieved at h=0.56. This value is even higher than t he theoretically predicted highest value of h=0.5. We also show that a maxi mum flux pinning can be achieved in the whole magnetic field when very fine secondary phase particles are dispersed in a superconducting (Nd, Eu, Gd)B a2Cu3Oy matrix with an optimum Nd: Eu: Gd ratio. (C) 2001 American Institut e of Physics.