Effects of interparticle interactions upon the magnetic properties of CoFe2O4 and MnFe2O4 nanocrystals

The interparticle distance has been systematically varied by controlling the concentration of 8-nm CoFe2O4 or MnFe2O4 spinet ferrite nanocrystals dispersed in eicosane. For both nanoparticulate systems, the blocking temperature decreased with increasing interparticle distance through dilution of nanocrystals, which suggests a decrease in the anisotropy energy barrier E-A. The blocking temperature for MnFe2O4 nanoparticles decreased continuously with decreasing nanocrystal concentration in eicosane. However, the blocking temperature for CoFe2O4 remained constant until similar to15% (wt %) concentration, below which the blocking temperature decreased sharply. The reduced remanence (M-R/M-S) decreased with decreasing interparticle distance for MnFe2O4, while it increased for CoFe2O4. The differences in magnetic response upon varying interparticle distance between the two systems are attributed to the strength of the dipole interactions. The behavior of the CoFe2O4 nanoparticulate system is consistent with the notion of nanoparticulate cluster formation.