An easy, low-cost, repeatable seed-mediated growth approach in solvothermal condition has been proposed to synthesize bimagnetic spinel ferrite core-shell heterostructures in the 10-20 nm particle size range. Cobalt ferrite and manganese ferrite nanoparticles (CoFe2O4 and MnFe2O4) have been coated with isostructural spinel ferrites like maghemite/magnetite, MnFe2O4, and CoFe2O4 with similar cell parameters to create different heterostructures. The conventional study of the structure, morphology, and composition has been combined with advanced techniques in order to achieve details on the interface at the nanoscale level. Clear evidence of the heterostructure formation have been obtained (i) indirectly by comparing the 57Fe Mössbauer spectra of the core-shell samples and an ad hoc mechanical mixture and (ii) directly by mapping the nanoparticles' chemical composition by electron energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDX) in the scanning transmission electron microscopy mode (STEM). In addition, chemical-sensitive electron tomography in STEM-EDX mode has been applied in order to obtain detailed 3D images with a sub-nanometer spatial resolution.

AS CR Inst Inorgan Chem vvi Husinec Rez 25068 Czech Republic

Center for Functional Nanomaterials Brookhaven National Laboratory Upton New York 11973 United States

Consorzio AUSI Palazzo Bellavista Monteponi 09016 Iglesias Italy

Department of Chemical and Geological Sciences Università di Cagliari S S 554 bivio per Sestu 09042 Monserrato Italy

Department of Inorganic Chemistry Charles University of Prague Staré Mesto 11636 Czech Republic

INSTM Cagliari Unit Via Giuseppe Giusti 9 50121 Firenze Italy

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