Magnetic-field-assisted layer-by-layer electrostatic assembly of ferromagnetic nanoparticles.

We report that layer-by-layer (LbL) electrostatic assembly of Fe(3)O(4) nanoparticles can be supplemented by orienting magnetic domains of the nanoparticles. With the oriented domains of ionic-capped nanoparticles, both magnetic and electrostatic forces of attraction become operative during the LbL deposition process. The magnetic-field-assisted LbL adsorption process has been evidenced by increased electronic absorbance of the films. While atomic force microscopy studies rule out formation of multiple layers during a single adsorption process, magnetic force microscopy images evidence oriented domains in the LbL films. The results show a novel route for LbL deposition of ferromagnetic nanoparticles with oriented magnetic domains in the thin films.