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RESEARCH PAPER

Microstructure and paramagnetic Meissner effect of YBa2 Cu3 Oy nanowire networks A. L. Pessoa · A. Koblischka-Veneva · C. L. Carvalho · R. Zadorosny · M. R. Koblischka

Received: 11 May 2020 / Accepted: 29 October 2020 © The Author(s) 2020

Abstract The microstructure and magnetic characterizations of non-woven, fabric-like YBa2 Cu3 Oy (YBCO) nanofiber mats are reported. The samples were produced by solution blow spinning (SBS), starting from a sol-gel solution of the precursor materials in polyvinylpyrrolidone. In the present work, the nanowire network samples were morphologically characterized by scanning electron microscopy, and the superconducting properties were measured by magnetometry. An interesting feature is the appear-

ance of a paramagnetic Meissner effect (PME) when field-cooling, firstly verified in that sort of sample. The PME appears only in very small applied magnetic fields, which is similar to previous observations of the PME on an artificially granular YBCO thin film, but distinctly different from bulk samples investigated in the literature. Thus, we explain the PME by flux trapping within the voids of the nanoporous structure of the nanofiber mats. Keywords Paramagnetic Meissner effect · Solution blow spinning · YBCO nanofiber mats

A. L. Pessoa · C. L. Cavalho · R. Zadorosny Superconductivity and Advanced Materials Group, School of Engineering, S˜ao Paulo State University (UNESP), Campus at Ilha Solteira, Ilha Solteira, Brazil e-mail: [email protected] C. L. Cavalho e-mail: [email protected] R. Zadorosny e-mail: [email protected] A. Koblischka-Veneva · M. R. Koblischka () Experimental Physics, Saarland University, Saarbr¨ucken, Germany e-mail: [email protected] A. Koblischka-Veneva e-mail: [email protected] Present Address: A. Koblischka-Veneva · M. R. Koblischka Shibaura Institute of Technology, Tokyo, Japan

Introduction Since the discovery of ceramic superconductors (HTSc), a variety of applications have been proposed (Seeber 1999; Seidel 2015). However, there are still persistent implementation difficulties of the present day HTSc materials, which are related to low transport current densities, high ac-losses, their brittleness, and the high production costs (Bray 2009). For massive, bulk materials required for trapped field applications (Cardwell et al. 2004), the oxygenation processes and the cooling of the samples can also be a problem (Reddy and Schmitz 2002; Haran et al. 2017). Thus, focusing on a more accessible material to be cooled, high-porous superconductors can be good specimens to be studied (Koblischka and Koblischka-Veneva 2018).

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In this point of view, superconducting nanowire networks of YBa2 Cu3 O7−δ (YBCO) were prepared by the solution blow spinning (SBS) technique (Daristotle et al. 2016; da Costa Farias et al. 2015; Cheng et al. 2014). The resulting samples are fabric-like networks or fiber mats of nanowires, being very similar to the nanowire network samples fabricated by electrospinning of YBCO (Duarte