Flux pinning in large NdBa2Cu3O7-δ grains fabricated by seeded-melt growth

The magnetization of top seeded-melt processed NdBa2Cu3O7-delta (Nd-123) containing 15 mol % Nd4Ba2Cu2O10 (Nd-422) has been investigated by vibrating sample magnetometry over a wide temperature (50 K< T<94 K) and field (0<mu(0)H<12T) range. The origin of the peak in the M-H loops and high irreversibility field values observed in this system are discussed on the basis of these data. The normalized pinning force determined from the hysteresis width is observed to scale as a function of reduced magnetic field (h =H/H-irr) and exhibits a peak at h(max)=0.33, suggesting that normal defects dominate the pinning mechanism in this material. This is in contrast with other recent reports of NdBa2Cu3O7-delta, which suggest that the peak effect is associated with a local variation in superconducting transition temperature due to the formation of a distributed solid-solution phase in the Nd-123 matrix.