Magnetic properties of single biogenic magnetite nanoparticles

Biogenic magnetite nanoparticles (MNP) extracted from the magnetotactic bacterium Magnetospirillum gryphiswaldense MSR-1 have been systematically studied by atomic force microscopy (AFM) and magnetic force microscopy (MFM). Isolated single MNP and chains of MNP were obtained from diluted MNP aqueous suspension dried on mica surfaces in a homogeneous in-plane magnetic field. The size of the MNP was determined by employing AFM tip deconvolution procedures. The obtained result has been confirmed by scanning electronic microscopy. Magnetic properties of isolated single MNP and chains of MNP in remanence and in the presence of external magnetic fields were investigated by MFM. In particular, the magnetization reversal of a two-particle chain has been revealed and the dipolar interaction between the MNP is estimated. The change in the magnetic contrast on application of an external magnetic field is consistent with the hysteresis curve obtained by cantilever magnetometry.