Synthesis of magnetic spinel ferrite CoFe2O4 nanoparticles from ferric salt and characterization of the size-dependent superparamagnetic properties

The CoFe nanoparticles have been synthesized by using a stable ferric salt of FeCl with a micellar microemulsion method. The normal micelles are formed by sodium dodecyl sulfate (NaDS) in aqueous solutions. The mean size of the nanoparticles can be controlled from less than 4 nm to about 10 nm through controlling the concentrations of the reagents. The neutron diffraction in combination with the Rietveld refinement shows that these CoFe nanoparticles have a high degree of inversion with 66% of the tetrahedral sublattice occupied by Fe . Magnetic measurements and neutron diffraction studies demonstrate the superparamagnetic nature of these CoFe nanoparticles. The size-dependent superparamagnetic properties of CoFe nanoparticles have also been systematically studied. The blocking temperature and coercive field of the nanoparticles increase with increasing size of the nanoparticles. The superparamagnetic behaviors of CoFe nanoparticles are consistent with the Stoner-Wohlfarth theory of single domain particles.