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Magnetic and structural characterization of nanostructured hollow spheres of cobalt, zinc, manganese and nickel ferrites syntetized using the hydrothermal method

Abstract:

Hollow nanostructured spheres of Co, Zn, Mn and Ni ferrites were synthesized from metallic impregnation in situ during the formation of colloidal carbon microspheres from hydrothermal treatment of a glucose solution at 160 °C for 24h and then calcinated in air at 550 °C for 2h. The X-ray diffraction powder patterns reveal the formation of spinel-like crystalline ferrites as single phase, except for Zn derivative, which is observed the formation of ZnO additionally. The characterization by Scanning Electronic Microscopy and Transmission Electronic Microscopy showed that resulting solids consist of welldefined hollow microspheres with a external diameter size distribution between 0.4 ≤ de ≤8.1 μm. The Ferromagnetic Resonance (FMR) shows the characteristic Superparamagnetic behaviour of the nanoparticles that conform the microstructures of the spheres. In the ZnFe2O4 sample there are two FMR signals, the low field signal is attributed to the Superparamagnetic behaviour and the high field signal belongs together with a ferromagnetic attributable transition to ZnO, in agreement with that observed by X-ray diffraction. The CoFe2O4 shows a hysteresis loop characteristic of ferromagnetic order.