A Two‐Parameter Model for Colloidal Particles with an Extended Magnetic Cap

Abstract

Self‐assembly of magnetic colloidal particles in solution has successfully been simulated by hard‐ or soft‐sphere models with a set of embedded magnetic point dipoles, and the position and orientation of each dipole are adapted to mimic the magnetization distribution. Herein, a conceptually simpler approach is introduced for magnetically capped colloidal particles, which replaces the set of dipoles by the extended magnetization distribution of a single conductive loop. Only two parameters are required to characterize the magnetization distribution: the diameter of the loop and its radial off‐center shift within the sphere. This approach reflects the radial symmetry and the spatial extension of the magnetic cap. At larger distance and in the limit of very small loops that model reproduces the far field and particle arrangements obtained with the single, radially shifted dipole model. For larger loop radii, additional stable assembly patterns are obtained, which occur in experiments, but cannot be simulated with a single shifted dipole model.