Magnetic colloids composed of metal nanoparticles of Fe

High magnetization, oil-based magnetic colloids (or magnetic fluids) have been fabricated with metallic Fe nanoparticles. These particles remain unchanged for several years in oil, water and air, etc. These particles have a core-shell structure. The shell is an epitaxial γ-Fe2O3 layer of 4 nm. It is the epitaxial oxide layer that prevents the metal core from further oxidization. Therefore, these particles show a much higher magnetization than Fe3O4 and γ-Fe2O3 particles, which are traditional materials for making ferrofluids. The preliminary results indicate that with these metallic Fe nanoparticles the magnetization of the colloids increases significantly.