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A Two-Parameter Model for Colloidal Particles with an Extended Magnetic Cap
Neumann, M.; Strobel, A.; Al-Saadawi, Y.; Steinbach, G.; Erbe, A.; Gemming, S.;
Self-assembly of magnetic colloidal particles in solution has succesfully 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. The present study introduces a conceptually simpler approach for magnetically capped colloidal particles, which replaces the set of dipoles by the 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. In the far-field and in the limit of very small loops the model exactly reproduces the magnetization distribution and the 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 can not be simulated with a single shifted dipole model.
Keywords: colloids, colloidal suspensions, magnetic colloidal particles, 2D assembly, self-assembly, effective Hamiltonians, theory, mesoscopic materials, soft-sphere potential, shifted-dipole model

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Publ.-Id: 29568 - Permalink