A metastable phase crystallized from undercooled NdFeCoZrGaB alloy droplets

Cobalt ferrite nanoparticles have been prepared by the combination of chemical precipitation, mechanical alloying and subsequent heat treatment. Sodium chloride was added before milling in order to avoid agglomeration. From XRD measurements it was found that the cobalt ferrite phase could form directly during mechanical milling of the precipitated hydroxide/oxidhydroxide precursor. Long-term milling caused contamination and growth in particle size. In order to reduce these two undesirable effects, a revised processing route, milling at a lower speed for a relatively shorter time and further heat treatment, was adopted. CoFe2O4 nanoparticles were obtained after a simple washing process with deionised water. TEM measurements showed that the nanoparticles had a fairly uniform structure and a mean particle size of approximately 10 nm. Anisotropic nanoparticles were obtained after magnetic annealing at 300°C.