Flux pinning in ternary (Nd0.33Eu0.33Gd0.33)Ba2Cu3Oy melt-processed, superconductors

The flux pinning characteristics of ternary melt-processed (Nd0.33Eu0.33Gd0.33)Ba2Cu3Oy (NEG) superconductors are studied in the temperature range 60 less than or equal to T less than or equal to 90 K. 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 h(0) = 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. (C) 1998 American Institute of Physics. [S0003-6951(98)01742].