Flux pinning in melt-processed ternary (Nd-Eu-Gd)Ba₂Cu₃O_y superconductors with Gd₂BaCuO₅ addition

The flux pinning behavior of ternary melt-processed (Nd-Eu-Gd)Ba₂Cu₃O_y superconductors is studied with varying Gd₂BaCuO₅ second-phase (Gd-211) defect concentrations using magnetotransport and magnetization measurements. The critical current density, J_c increases with the addition of Gd-211 particles displaying a maximum value of J_c for 30% at zero and in intermediate field range and decreases on further addition of Gd-211 particles. A pronounced field-induced bump feature in the resistivity was observed. The dynamic scaling of the resistance suggests the low temperature phase as the vortex-glass phase. The current-voltage characteristics over the whole transition temperature regime show a linear flux-flow type behavior that favors the phenomenon of vortex entanglement in the liquid phase. The Nd/Ba substitution sites along with Gd-211 second-phase particles refined by the addition of a small amount of Pt are one of the possible reasons for the vortex entanglement in the liquid phase. The in-plane and out-of-plane resistance measurements clearly show the correlation of the vortices in the liquid state favoring some influence of twin planes and occasionally occurring natural grain boundaries on the liquid state as well. These defects give rise to high critical current density at low temperature with significant enhancement in pinning favoring the glassy phase to occur.