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Pure Appl. Chem. Vol. 72, Nos. 1-2, p. 37-45, 2000

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

Chao Liu, Adam J. Rondinone, and Z. John Zhang*

*School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA

Abstract: The CoFe₂O₄ nanoparticles have been synthesized by using a stable ferric salt of FeCl₃ 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 CoFe₂O₄ nanoparticles have a high degree of inversion with 66% of the tetrahedral sublattice occupied by Fe₃₊. Magnetic measurements and neutron diffraction studies demonstrate the superparamagnetic nature of these CoFe₂O₄ nanoparticles. The size-dependent superparamagnetic properties of CoFe₂O₄ 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 CoFe₂O₄ nanoparticles are consistent with the Stoner-Wohlfarth theory of single domain particles.

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