Reverse micelle synthesis and characterization of superparamagnetic MnFe₂O₄ spinel ferrite nanocrystallites

MnFe₂O₄ nanoparticles are synthesized by using sodium dodecylbenzenesulfonate (NaDBS) to form water-in-toluene reverse micelles. The nanoparticles are single crystalline, and the average particle size can be controlled from 4 to 15 nm. High- and low-resolution transmission electron microscopy characterization has shown that the nanoparticles can have a size distribution as narrow as ∼9%. Neutron diffraction and magnetic measurements have been conducted on the nanoparticles with a diameter of 7.7 ± 0.7 nm. The results unambiguously prove that these MnFe₂O₄ nanoparticles are truly superparamagnetic. The synthesis and characterization of these nanoparticles will facilitate the development of MnFe₂O₄ nanoparticles for the potential applications such as contrast enhancement agents of magnetic resonance imaging and magnetic carriers for site-specific drug delivery.