Doublet dynamics of magnetizable particles under frequency modulated rotating fields

We study experimentally the dynamics of an isolated pair of paramagnetic micro-particles when applying rotating and frequency modulated magnetic fields. In the case of purely rotating field, the inter-particle distance performs radial oscillations above a given threshold. The oscillation threshold depends on the viscosity and the amplitude of the magnetic field. When the data are represented in terms of the relative distance to the critical Mason number all curves collapse nicely. The master curve obtained shows the same features that are obtained in numerical simulations. For frequency modulated rotating fields, complex and irregular dynamics is obtained. This dynamics is again in qualitative agreement with numerical simulations.