Institute of Physics, Technische Universität Chemnitz, 09107 Chemnitz, Germany.
Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, 01328 Dresden, Germany.
Phys Rev E. 2019 Jul;100(1-1):012608. doi: 10.1103/PhysRevE.100.012608.
Particle dispersions provide a promising tool for the engineering of functional materials that exploit self-assembly of complex structures. Dispersion made from magnetic colloidal particles is a great choice; they are biocompatible and remotely controllable among many other advantages. However, their dominating dipolar interaction typically limits structural complexity to linear arrangements. This paper shows how a magnetostatic equilibrium state with noncollinear arrangement of the magnetic moments, as reported for ferromagnetic Janus particles, enables the controlled self-organization of diverse structures in two dimensions via constant and low-frequency external magnetic fields. Branched clusters of staggered chains, compact clusters, linear chains, and dispersed single particles can be formed and interconverted reversibly in a controlled way. The structural diversity is a consequence of both the inhomogeneity and the spatial extension of the magnetization distribution inside the particles. We draw this conclusion from calculations based on a model of spheres with multiple shifted dipoles. The results demonstrate that fundamentally new possibilities for responsive magnetic materials can arise from interactions between particles with a spatially extended, anisotropic magnetization distribution.
粒子分散体为工程功能材料提供了有前途的工具，这些材料利用复杂结构的自组装。由磁性胶体粒子制成的分散体是一个很好的选择；它们具有生物相容性和许多其他优点，如远程可控性。然而，它们的主导偶极相互作用通常将结构复杂性限制在线性排列。本文展示了如何通过静磁平衡状态实现非共线的磁矩排列，如报道的铁磁 Janus 粒子所示，这使得通过恒温和低频外磁场在二维空间中控制各种结构的自组织成为可能。交错链的分支簇、紧密簇、线性链和分散的单个粒子可以以可控的方式形成和可逆地相互转换。结构多样性是粒子内部磁化分布的不均匀性和空间延伸的结果。我们从基于具有多个偏移偶极子的球体模型的计算中得出了这一结论。结果表明，具有空间扩展各向异性磁化分布的粒子之间的相互作用可以为响应性磁性材料带来全新的可能性。
