High Tc superconductor–ferromagnetic heterostructures constitute an appealing playground to study the interplay between flux vortices and magnetic moments. Here, the capability of a solution-derived route to grow hybrid YBa2Cu3O7-ferromagnetic nanocomposite epitaxial thin films from preformed spinel ferrite (MFe2O4, M = Mn, Co) nanoparticles (NPs) is explored. The characterization, performed using a combination of structural and magnetic techniques, reveals the complexity of the resulting nanocomposites. Results show that during the YBCO growth process, most of the NPs evolve to ferromagnetic double-perovskite (DP) phases (YBaCu2−x−yFexCoyO5/YBaCoFeO5), while a residual fraction of preformed ferrite NPs may remain in the YBCO matrix. Magnetometry cycles reflect the presence of ferromagnetic structures associated to the DPs embedded in the superconducting films. In addition, a superparamagnetic signal that may be associated with a diluted system of ferromagnetic clusters around complex defects has been detected, as previously observed in standard YBCO films and nanocomposites. The hybrid nanocomposites described in this work will allow studying several fundamental issues like the nucleation of superconductivity and the mechanisms of magnetic vortex pinning in superconducting/ferromagnetic heterostructures.

The authors acknowledge financial support from Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496), CONSOLIDER Excellence Network (MAT2015-68994-REDC), COACHSUPENERGY project (MAT2014-51778-C2-1-R, cofinanced by the European Regional Development Fund), and from the Catalan Government with 2014-SGR-753 and Xarmae. Some of the electron microscopy work has also been conducted in the Laboratorio de Microscopías Avanzadas (LMA) at Instituto de Nanociencia de Aragón (INA) at the University of Zaragoza. Part of the electron microscopy work in EMAT group (University of Antwerp) was performed within the framework of the EUROTAPES project (FP7-NMP.2011.2.2-1 Grant No. 280432), funded by the European Union. Work at INA-LMA was supported by NanoAraCat. Research at UCM (J.S.) was supported by the ERC starting Investigator Award, Grant No. 239739 STEMOX and Juan de la Cierva Program JCI-2011-09428 (MICINN-Spain). The XMCD experiments were performed at the BOREAS beamline of the ALBA Synchrotron Light Facility with the collaboration of ALBA staff. The authors would like to thank SOLEIL synchrotron for allocating beamtime and the DiffAbs beamline staff for help during the experiments.

Peer reviewed