Flux pinning in ternary (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu ₃O_y melt-processed superconductors

The flux pinning characteristics of ternary melt-processed (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu ₃O_y (NEG) superconductors are studied in the temperature range 60≤T≤90K. NEG samples exhibit a strongly developed peak effect in the dependence of the critical current densities on the external field, H_a. The scaling of the pinning forces versus the reduced field h=H_a/H_irr (where H_irr denotes the irreversibility field) yields a peak at h₀=0.5 which is an indication of pinning provided by a spatial variation of the transition temperature. The presence of a weaker superconducting second phase is demonstrated by means of field cooling and warming experiments in fields up to 7 T. Furthermore, we discuss the possible effect of the magnetic moments of Gd and Nd on the flux pinning.