To clarify the optimization of matrix chemical ratio for high critical current density Jc in (Nd, Eu, Gd)Ba2Cu3Oy superconductors using flux creep-flow model

The magnetic field dependence of critical current density Jc for a group of specimens of (Nd, Eu, Gd)Ba2Cu3Oy superconductors with changing matrix chemical ratio such as Eu/Gd ratio was estimated from the hysteresis measurements by using the Bean model. The highest peak critical current density Jcp, was observed for (Nd0.33Eu0.39Gd0.27)Ba2Cu3Oy specimen with addition of 3 mol% NEG-211 particles and it was about 1.77 x 109 A/m2 at higher magnetic field of 2.5T. To clarify the speculation about the optimization of the peak critical current density Jcp, the experimental results are compared with the theoretical analysis based on flux creep-flow model taking the distribution of the flux pinning strength into account. The number of flux lines in the flux bundle (g2), the most probable value (Am), the distribution width (σ2) and the other pinning parameters m, γ are determined so that a good fit is obtained between the experimental and theoretical results. The higher the value of Am of sample 3 mol% NEG-211 phase particles (i.e., the higher value of peak critical current density, Jcp) than 7 mol% addition sample suggests that it is justified the speculation about the optimization of the peak critical current density Jcp, due to the maximum pinning effect caused by combining the appropriate concentration of 211 secondary phase particles with the optimum chemical ratio in the matrix. (author)