Mesoscopic organizations of magnetic nanocrystal: the influence of short-range interactions

The organization of magnetic nanoparticles is an ideal model system to study the interplay of short-range isotropic and long-range anisotropic forces. A Brownian dynamics method is presented to model the evaporation of magnetic nanoparticle solutions subjected or not to an applied magnetic field. The simulation results show a marked dependence of the final nanoparticle organizations with van-der-Waals interactions tuned by the thickness of the particle coating. In spite of weak dipole–dipole interactions between the magnetic nanoparticles studied here, even chain-like organizations appear when the nanoparticle solution is evaporated under magnetic field. The theoretical results are in good agreement with experimentally observed organizations of maghemite nanoparticles, where the particle contact distance is tuned by the length of the molecules coating the particles. Finally, the new simulation technique is compared to other methods used to study aggregation in dipolar systems and its advantages and drawbacks are discussed.