Tunable interactions between paramagnetic colloidal particles driven in a modulated ratchet potential

Abstract

We study experimentally and theoretically the interactions between paramagnetic particles dispersed in water and driven above the surface of a stripe patterned magnetic garnet film. An external rotating magnetic field modulates the stray field of the garnet film and generates a translating potential landscape which induces directed particle motion. By varying the ellipticity of the rotating field, we tune the inter-particle interactions from net attractive to net repulsive. For attractive interactions, we show that pairs of particles can approach each other and form stable doublets which afterwards travel along the modulated landscape at a constant mean speed. We measure the strength of the attractive force between the moving particles and propose an analytically tractable model that explains the observations and is in quantitative agreement with experiment.

11 pages, 6 figures, submitted

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• Synchronous versus asynchronous transport of a paramagnetic particle in a modulated ratchet potential
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• Functional colloidal micro-sieves assembled and guided above a channel-free magnetic striped film
• Memory effects in colloidal motion under confinement and driving
• Novel structure formation of a phase separating colloidal fluid in a ratchet potential
• Stability of paramagnetic spheroid in precessing field
• Self-assembly and percolation in magnetic colloids