Paramagnetic colloids in rotating fields: from chains through chaos to clusters.

We present computer simulations and experiments on dilute suspensions of superparamagnetic particles subject to rotating magnetic fields. ~We focus on short chains of particles and their decay routes to stable structures. ~At low rate, the chains track the external field. ~At intermediate rate, the short chains break up but perform a periodic (albeit complex) motion. ~At sufficiently high rates, the chains generally undergo chaotic motion at short times and decay to either close-packed clusters or more dispersed colloidal~``molecules'' at long times. ~We show that the transition out of the chaotic states follows a first order reaction kinetics.