This work deals with the synthesis of superparamagnetic cobalt ferrite (CoFe 2 O 4 ) nanoparticles, via a sol-gel method that uses gelatin as an organic precursor and a rapid thermal processing furnace with halogen lamps as a heat source. TEM, HRTEM, XRD, VSM and Mössbauer spectroscopy measurements were performed, at room temperature, to characterize the samples. Nanoparticles with an average size of 5-10 nm and microstrain of the order of 10 −4 -10 −3 were obtained. Magnetic hardening was also observed with increased nanoparticle size, in addition to an increase in the anisotropy constant, which ranged from 1.7 to 4.7•10 6 erg/cm 3 . The saturation magnetization decreased with decreasing size due to the formation of a magnetically dead layer on the surface (thickness = 0.6-0.7 nm). The Mössbauer spectra showed an increase in the superparamagnetic phase for samples with smaller nanoparticles and less dispersion.
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