Magnetic properties of the nanocomposite CoFe₂O₄/FeCo-FeO at a high H/T regime

The low temperature magnetic properties of nanopowders of CoFe₂O₄ and of CoFe₂O₄/FeCo-FeO with average particle size of about 6 nm were investigated for temperatures down to 5 K and for applied magnetic fields up to 350 kOe. Highly enhanced coercive fields were obtained for the CoFe₂O₄ nanoparticles. The values of the saturation magnetization M_S and of the anisotropy constant K₁ were also found to be enhanced for the nanocomposite powder sample. The overall results are discussed in terms of a particle model which takes into account a thin amorphous layer present in the CoFe₂O₄ particles and due to a FeCo-FeO layer grown during an annealing procedure. Moreover, the temperature dependence of K₁ was found to be in good agreement with a model proposed by Tachiki. - Highlights: • The magnetic properties of ferrites were investigated in a high H/T regime. • The nanopowders showed the largest anisotropy constant value found so far. • No other previous work reported this kind of study in cobalt ferrites.