Magnetic moment and volume fraction controlling chain-like structures of magnetic nanoparticles in uniform magnetic fields

The magnetically assembled chain-like structures of magnetic nanoparticles attract great attention due to their unique properties. In this paper, we studied the influences of essential magnetic controlling parameters on the chain-like structures of magnetic nanoparticles with diameter d = 360 nm using a 3D Monte Carlo simulation. The magnetic moment and volume fraction of magnetic nanoparticles were found to play crucial roles in the arrangement of the nanoparticles. The simulation results were in agreement with experimental evidence, summarized as follows: In the limit of low magnetic moment m < 3.7×10⁻¹⁶ A∙m², magnetic nanoparticles did not linearly arrange along the direction of the magnetic field but formed aggregates. At magnetic moment m > 1.5×10⁻¹⁵ A∙m² and volume fraction φ<0.02%, the formation effect of nanochains consisting of individual particles was first enhanced and then remained almost unchanged with increasing magnetic moment. For magnetic moment m>7.3×10⁻¹⁵ A∙m² and volume fraction φ>1%, nanochains gradually coarsened into the nanobundles with increasing volume fraction. The results can provide a theoretical basis to construct and regulate other assembled structures consisting of building blocks.