Evidence for largest room temperature magnetic signal from Co2+ in antiphase-free & fully inverted CoFe2O4 in multiferroic-ferrimagnetic BiFeO3-CoFe2O4 nanopillar thin films

The ongoing quest for defect-free thin films systems that are apt for being used as spin filtering materials for spintronic applications did yet not deliver satisfying results regarding materials that would be up to the pertinent requirements. Using soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at the Co-L_2,3 and Fe-L_2,3 absorption edges, we have investigated the magnetic properties of a nanostructured thin film with self-assembled CoFe₂O₄ nanopillars embedded in BiFeO₃, the latter being a well-known system for its combined multiferroic and spintronic properties. In this BiFeO₃-CoFe₂O₄ heterostructure we observed a significant XMCD signal at the Co-L_2,3 edges which turns out to be the largest among the presently reported for Co ions at room temperature. A quantitative analysis of the Co-L_2,3 spectra unveils that such a large Co-L_2,3 XMCD signal stems from the impeccable fully inverted spinel ordering of the A- and B-sites in antiphase-free CoFe₂O₄ nanopillars. This twofold perfect CoFe₂O₄ ordering feature yields an unprecedented optimization within a multifunctional ferrimagnetic-multiferroic thin film system highly relevant for spintronic applications, also resulting in an equally unprecedented macroscopic magnetic moment for such material as compared to its pure form as well as to technologically relevant thin film compound systems.