Enhancement of critical current density in (Nd, Eu, Gd)-Ba-Cu-O superconductors

We have achieved a large critical current density (J(c)) of 70000 A/cm² at 77 K in 2.3 T and a large irreversibility field exceeding 7 T at 77 K for the fields parallel to the c axis in (Nd, Eu, Gd)-Ba-Cu-O in which 40 mol% (Nd, Eu, Gd)₂BaCuO₅ (NEG211) second phase particles are finely dispersed in the (Nd, Eu, Gd)Ba₂Cu₃O(y) matrix and prepared by the melt process under oxygen partial pressure of 0.1%. Microstructural observations clarified that Pt addition was effective in reducing the size of NEG211 second phase particles, which led to a dramatic increase in J(c). A clear secondary peak effect was observed in the magnetization curve, suggesting that field-induced pinning is active in parallel with the pinning by NEG211 particles.