A Detailed Investigation of the Onion Structure of Exchanged Coupled Magnetic Fe_3??O₄@CoFe₂O₄@Fe_3??O₄ Nanoparticles

Nanoparticles (NPs) which combine several magnetic phases offer wide perspectives for cutting edge applications because of the high modularity their properties. Besides addition characteristics intrinsic to each phase, interface that results from core-shell and, further, onion structures leads synergistic properties such as exchange coupling. Such a phenomenon is interest overcome superparamagnetic limit iron oxide NPs hampers potential applications. In this manuscript, we report on design with an onion-like structure have been scarcely reported yet. These consist in Fe(3_delta)O4 core covered by first shell CoFe2O4 and second Fe(3-delta)O4. They were synthesized multi-step seed mediated growth approach. Although TEM micrographs clearly show core, sizes thicknesses markedly differ what suggested size increase. We investigated very precisely performing resolution (scanning) imaging GPA. The chemical composition spatial distribution atoms studied EELS. environment oxidation state cations M\"ossbauer spectrometry, soft XAS XMCD. techniques allowed us estimate increase Fe2+ content core@shell cobalt ferrite thickness core@shell@shell one, while appears be much thinner than expected. Thus, modification well Fe(3-delta)O4 impact Furthermore, also modifies NPs.