1. Duke University, Department of Mechanical Engineering and Materials Science, Center for Biologically Inspired Materials and Material Systems, Box 90300, Hudson Hall, Durham, North Carolina 27708, USA
2. Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003, USA
3. These authors contributed equally to this work.

Correspondence to: Benjamin B. Yellen¹ Correspondence and requests for materials should be addressed to B.B.Y. (Email: yellen@duke.edu).

The assembly of complex structures out of simple colloidal building blocks is of practical interest for building materials with unique optical properties (for example photonic crystals¹ and DNA biosensors²) and is of fundamental importance in improving our understanding of self-assembly processes occurring on molecular to macroscopic length scales^{3, 4, 5}. Here we demonstrate a self-assembly principle that is capable of organizing a diverse set of colloidal particles into highly reproducible, rotationally symmetric arrangements. The structures are assembled using the magnetostatic interaction between effectively diamagnetic and paramagnetic particles within a magnetized ferrofluid. The resulting multipolar geometries resemble electrostatic charge configurations such as axial quadrupoles ('Saturn rings'), axial octupoles ('flowers'), linear quadrupoles (poles) and mixed multipole arrangements ('two tone'), which represent just a few examples of the type of structure that can be built using this technique.

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