Kinetics of aggregation of 50 nm-sized magnetic nanoparticles

We present experimental and theoretical results about kinetics of aggregation of Brownian magnetizable particles of a mean size of 50 nm in the presence of a uniform magnetic field. In experiments, field-induced micron-sized string-like aggregates has been observed directly using optical microscopy. This method allows the determination of the time dependency of the length and the thickness of the aggregates at different magnetic field intensities. Two principle mechanisms of the aggregate growth have been established: adsorption of single particles by the aggregates and coalescence of aggregates, while Oswald ripening seems to take place at much longer time scales. Experimental results are in quantitative agreement with the developed theoretical model.