Elaboration of superparamagnetic cobalt-ferrite nanocomposites from films of chitosan chelates

Cobalt-ferrite nanocomposites were synthesized from polymeric films of chelates of Co(II) and Fe(III) ions within a chitosan matrix by a solid-state coprecipitation reaction with weight content ratios of chitosan to cobalt- ferrite of 50/50 and 25/75 w/w. Morphological and crystalline studies of the composites were performed by high-resolution transmission electron microscopy, X-ray diffraction, and selected area electron diffraction with a nanobeam diffraction probe. The results show nanoparticles around 4 nm with a spinel structure, consistent with the cobalt- ferrite phase. The magnetic behavior was evaluated with curves of the applied-field-dependent magnetization [M(H)] and the temperature-dependent magnetization [M(T)]. Both the M(H) and M(T) curves showed typical superparamagnetic behavior, depicting an absence of hysteretic characteristics and the characteristic peak at blocking temperature in the zero-field-cooled curve. There was also evidence of strong interparticle and intraparticle interactions, which suggested magnetic frustration in the particle magnetic moment alignment with the applied field.