Paramagnetic effect at low and high magnetic fields in melt-texturedYBa2Cu3O7−δ

Abstract

We report on systematic field-cooled magnetization experiments in five different melt-textured $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ samples containing large amounts of ${\mathrm{Y}}_{2}\mathrm{Ba}\mathrm{Cu}{\mathrm{O}}_{5}$ precipitates. These composites were grown with the Bridgman or top-seeding techniques. Fields ranging from $1\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}$ up to $50\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ were applied either parallel or perpendicular to the $\mathrm{Cu}\ensuremath{-}{\mathrm{O}}_{2}$ 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 $\mathrm{Cu}\ensuremath{-}{\mathrm{O}}_{2}$ 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 ${\mathrm{Y}}_{2}\mathrm{Ba}\mathrm{Cu}{\mathrm{O}}_{5}$ particles plays a crucial role in the explanation of this effect in the melt-processed $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ materials.