Superparamagnetic sub-5 nm Fe@C nanoparticles: isolation, structure, magnetic properties, and directed assembly.

A method for isolating single crystalline sub-5 nm carbon coated iron nanoparticles (Fe@C NPs) from a carbon nanotube matrix has been developed. The isolation of such particles allows for their characterization by high resolution electron microscopy methods and SQUID magnetometry. While the NPs are superparamagnetic at room temperature, at 10 K they exhibit a coercivity nearly 30 times greater than that of commercial Fe3O4 NPs of comparable size. A novel nanotemplate directed assembly method for manipulating the particles at the individual particle level is also reported.