Paramagnetic effect at low and high magnetic fields in melt-textured YBa/sub 2/Cu/sub 3/O/sub 7-[delta]/

Abstract

We report on systematic field-cooled magnetization experiments in five different melt-textured YBa2Cu3O7 samples containing large amounts of Y2BaCuO5 precipitates. These composites were grown with the Bridgman or top-seeding techniques. Fields ranging from 1 Oe up to 50 kOe were applied either parallel or perpendicular to the Cu-O2 atomic planes. In the low field limit, we observed the paramagnetic Meissner effect (PME) in a Bridgman grown sample for the configuration where the field is oriented parallel to the Cu-O2 atomic planes. Contrasting with this unique observation at low fields, a paramagnetic response related to the superconducting state was observed in all of the studied samples when strong enough fields were applied in both orientations. This high-field paramagnetic effect shows some noticeable differences when compared to the most frequently reported PME at very low fields. In particular, the magnitude of the high-field paramagnetic moment increases when the field is augmented. Moreover, this effect shows a strong and anomalous relaxation, such that the paramagnetic moment increases as a function of the time. The anisotropy of the high-field paramagnetic moment depends on the sample microstructure, suggesting that pinning by the Y2BaCuO5 particles plays a crucial role in the explanation of this effect in the melt-processed YBa2Cu3O7 materials.