Magnetic stability against calcining of microwavesynthesized CoFe2O4 nanoparticles

High quality CoFe2O4 nanoparticles were synthesized using a one-pot, microwave assisted method, that allows forming stable colloidal solutions in alcoholic solvents, as required for the preparation by Chemical Solution Deposition of hybrid nanocomposite ferromagnetic-high Tc YBa2Cu3O7 superconducting films or devices. We have investigated how the thermal process necessary for the preparation of such epitaxial nanocomposites, involving high temperatures (800 °C) and oxygen partial pressures (1 atm), affects the structure and magnetic properties of the isolated nanoparticles. The NPs were fully characterised by XRD, SQUID, STEM-EELS and XMCD at four different stages of the thermal process. Results show that, despite intermediate changes in the cation distribution occur during the process, the final NP magnetization is stable against the thermal treatment. This result opens up perspectives for the preparation of hybrid YBCO films with embedded magnetic NPs using low-cost chemical-solution methods
Authors acknowledge the MICIN (NANOSELECT, CSD2007-00041 and MAT2014-51778-C2-1-R and FEDER), Generalitat de Catalunya (2014SGR 753 and Xarmae), ‘‘Severo Ochoa’’ Programme for Centres of Excellence in R&D (SEV-2015-0496), the CONSOLIDER Excellence Network (MAT2015-68994-REDC) and the EU (EU-FP7 NMP-LA-2012- 280432 EUROTAPES project). Electron microscopy performed at the Centro Nacional de Microscopı´a Electro´nica (UCM) was sponsored by the ERC Starting Investigator Award No. STEMOX#239739. J. G. and M. C. also acknowledge the Ramon y Cajal program (RYC-2012- 11709, RYC-2013-12448). The XMCD experiments were performed at the BOREAS beamline of the ALBA Synchrotron Light Facility with the collaboration of ALBA staff.