Elena Bartolomé, Pablo Cayado, Eduardo Solano,Cristian Mocuta, Susagna Ricart, Bernat Mundet, Marionna Coll, Jaume Gázquez, Alexander Meledin, Gustaaf van Tendeloo, Manuel Valvidares, Javier Herrero-Martín, Pierluigi Gargiani, Eric Pellegrin, Cesar Magén, Teresa Puig, Xavier Obradors. Adv. Electron. Mater. 2017, 1700037. DOI: 10.1002/aelm.201700037
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 PhD student Ferran Vallés Pérez visited the National High Magnetic Field Laboratory in Tallahassee (Florida, USA) to perform electrical transport measurements on the superconducting films grown at ICMAB up to 35T, one of the highest DC fields on the earth, generated using a maximum electrical power of 23.3 MW. The study of these superconducting films is indeed performed with the challenging idea to use them for the fabrication of electromagnets that will be capable to generate these high magnetic fields with much less power consumption.
Our PhD student, Jordi Martínez, has been awarded with the second prize for his poster, abstract and oral presentation entitled “Uncovering the surface chemistry of LnF3 nanoparticles” during the “Jornades Doctorals 2017“ organized by the Chemistry Department of the Universitat Autònoma de Barcelona (UAB).
Jordi Martínez is a predoctoral researcher doing his PhD thesis under the supervision of Susagna Ricart, from ICMAB, and Ramón Yañez, from the Chemistry Department of the UAB.
His research is devoted to the synthesis and characterization of LnF3 (lanthanide fluoride) nanoparticles. These nanoparticles are then used to nanostructure superconducting materials and providing them with different and interesting properties.
P. Cayado, C. F. Sánchez-Valdés, A. Stangl, M. Coll, P. Roura, A. Palau, T. Puig and X. Obradors*. Phys. Chem. Chem. Phys., 2017,19, 14129-14140. DOI: 0.1039/C7CP01855J0.1039/C7CP01855J
The kinetics of oxygen incorporation (in-diffusion process) and excorporation (out-diffusion process), in YBa2Cu3O6+x (YBCO) epitaxial thin films prepared using the chemical solution deposition (CSD) methodology by the trifluoroacetate route, was investigated by electrical conductivity relaxation measurements. We show that the oxygenation kinetics of YBCO films is limited by the surface exchange process of oxygen molecules prior to bulk diffusion into the films. The analysis of the temperature and oxygen partial pressure influence on the oxygenation kinetics has drawn a consistent picture of the oxygen surface exchange process enabling us to define the most likely rate determining step. We have also established a strategy to accelerate the oxygenation kinetics at low temperatures based on the catalytic influence of Ag coatings thus allowing us to decrease the oxygenation temperature in the YBCO thin films.