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 K-1 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 K-1 was found to be in good agreement with a model proposed by Tachiki.