Paramagnetic Meissner Effect and Current Flow in YBCO Nanofiber Mats

Microstructural and magnetic characterizations of YBa ₂ Cu ₃ O _7-δ nanowire fabric-like samples were performed. Fabric-like ceramic superconductors are nanoporous materials and can be applied, e.g., in magnetic shielding, since the porous morphology makes them extremely light-weight and effectively to be cooled. The samples were produced by the solution blow spinning (SBS) technique, starting from a sol-gel solution of the precursor materials in polyvinyl-alcohol. The morphology of the samples was characterized by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction with the aim to analyze the possible current paths. The magnetic hysteresis loops revealed typical polycrystalline behavior, and field-cooling in various small applied fields shows the presence of the paramagnetic Meissner effect (PME), but in a distinctly different way as compared to melt-texured Bi ₂ Sr ₂ CaCu ₂ O _8+δ or Nb.