Cobalt-ferrite nanoparticles: correlations between synthesis procedures, structural characteristics and magnetic properties

Cobalt-ferrite nanoparticles of size 10 to 15 nm have been synthesized in water-in-oil microemulsions (i.e., reverse micelles). When the Co/sup 2+//Fe/sup 2+/ molar ratio in the precursor solution reaches 1:1 and above, the resultant oxides are identified as having the cobalt ferrite structure. By increasing the Co/sup 2+//Fe/sup 2+/ molar ratio in the precursor from 1:1 to 2:1, the atomic ratio of Co:Fe in the resultant ferrite increases from 0.83 to 1.31. The Co site occupancy is also dependent on the Co/sup 2+//Fe/sup 2+/ molar ratio in the precursor. The materials are found to exhibit superparamagnetism. The blocking temperatures and coercivities are dependent upon the Co/sup 2+//Fe/sup 3+/ ratio, reaching values as high as 55 K and 7500 G at 10 K, respectively. The correlation between synthesis procedure, site occupancy and magnetic properties enables the control of materials properties through such synthesis.