Orientation dynamics of magnetorheological fluids subject to rotating external fields

The formation and orientation of field-induced structures in magnetorheolog ical (MR) fluids subject to rotating magnetic fields have been studied usin g two optical methods: scattering dichroism and small angle light scatterin g (SALS). The SALS patterns show how these chain-like aggregates follow the magnetic field with the same frequency but with a retarded phase angle for all the frequencies measured. Using scattering dichroism two different beh aviors for both, dichroism and phase lag. an found below or above a critica l frequency. Experimental results have been reproduced by a simple model co nsidering the torques balance on the chain-like aggregates.