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 MS 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.