Effect of oxygen content variation on flux pinning in Nd-Ba-Cu-O top-seeded melt grown superconductor

The magnetization of top-seeded melt grown NdBa2Cu3O7-δ (Nd123) containing 15 mol% Nd4Ba2Cu2O10 (Nd422) processed in both air and under 1% O2 in N2 has been investigated over a wide range of temperatures and fields. The sample processed in air exhibits a peak in the Jc(H) data in the temperature range 40-70 K, which is similar to that observed in a sample processed under reduced oxygen partial pressure at nearly the same reduced temperature (T/Tc) range. The appearance and position of the peak in the Jc(H) data are governed strongly by the oxygen content. Magnetization as a function of temperature measured under zero field and field-cooled conditions exhibit similar magnetic transition behaviour, despite the large difference in the Nd/Ba substitution level within these samples. Significantly, the basic features of the magnetization curves remain virtually the same when the oxygen content in the sample is varied. Comparison between NdBCO and YBCO superconductors indicates clearly that the defects associated with oxygen vacancies and/or disorder play an important role in flux pinning in both types of melt grown material. The pinning centres in NdBCO observed in this study are similar to those observed in YBCO. (author)