Scanning probe microscopy on magnetic colloidal particles

We report some first results on magnetite and iron nanoparticles studied with atomic force microscopy (AFM). AFM images the particles on a smooth substrate, and their lateral diameter, height and polydispersity are determined and discussed. The use of magnetic force microscopy (MFM) on such small particles is explored both experimentally and theoretically. We present models which allow to estimate with MFM the magnetic moment of a single superparamagnetic nanosphere, which cannot be done with other techniques.