Synthesis of magnetic spinel ferrite CoFe<sub>2</sub>O<sub>4</sub> nanoparticles from ferric salt and characterization of the size-dependent superparamagnetic properties

Liu, Chao; Rondinone, Adam J.; Zhang, Z. John

doi:10.1351/pac200072010037

Pure Appl. Chem., 2000, Vol. 72, No. 1-2, pp. 37-45

http://dx.doi.org/10.1351/pac200072010037

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.