New methods for inducing microscopic particles to assemble into useful macroscopicstructures could open pathways for fabricating complex materials that cannot be producedby lithographic methods. Here we demonstrate a colloidal assembly technique that uses twoparameters to tune the assembly of over 20 different pre-programmed structures, includingkagome, honeycomb and square lattices, as well as various chain and ring configurations. Weprogramme the assembled structures by controlling the relative concentrations and interactionstrengths between spherical magnetic and non-magnetic beads, which behave as paramagneticor diamagnetic dipoles when immersed in a ferrofluid. A comparison of our experimentalobservations with potential energy calculations suggests that the lowest energy configurationwithin binary mixtures is determined entirely by the relative dipole strengths and their relativeconcentrations.
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