Brownian Dynamics Simulations of Magnetic Nanoparticles Captured in Strong Magnetic Field Gradients

The behavior of spherical single-domain magnetic nanoparticles in strong inhomogeneous magnetic fields is investigated through Brownian dynamics simulations, taking into account magnetic dipole-dipole interactions, repulsive a, hard-core Yukawa potential, hydrodynamic particle-wall interactions, and the mechanism of magnetic dipole rotation in the presence of a magnetic field. The magnetic capture process of nanoparticles in prototypical magnetic field:gradients generated by a sudden reversal in perpendicular magnetization of a flat substrate (defining a capture line) is studied as a function of strength of the magnetic field and volume fraction of the magnetic nanoparticles. Capture curves show a regime where capture follows a power law model and suggest that particles with the Brownian relaxation mechanism are captured at a slightly faster rate than particles with the Neel relaxation mechanism under similar conditions of the field gradient. Additionally, evaluation of the shape of the aggregates of captured particles-suggests that greater dipole-dipole interactions, result in aggregate structures that are flatter/wider than in the case of negligible dipole-dipole interactions. These results can help guide the-design of systems for magnetically directed assembly of nanoparticles into complex shapes at a substrate.