Magneto-optic Effects in Ferrofluids

Ferrofluids are stable colloidal suspensions of superparamagnetic nanoparticles in a carrier liquid. The ordering and phase transitions of these polarizable media under the effect of an externally applied dc magnetic field are accompanied by a number of magneto-optic effects. Light scattering, in particular, has been used in studies investigating the kinematics of the field-induced self-assembly of nanoparticles in chain-like structures. In previous reports we discussed the correlation between the time-dependent light-scattering patterns and the creation of such field-induced ordered structures of nanoparticles in the ferrofluid. This present work is the first reported systematic study of the morphing of the light scattering patterns with the thickness of the ferrofluid layer (0.1 mm to 10 mm) and with temperature, in ferrofluids consisting of water suspensions of dextran-coated iron oxide nanoparticles. In particular we discuss the origin and angular dependence of an elliptical pattern produced by light scattered through thin layers (<;1 mm) of ferrofluids and contrast it with the patterns produced by longer light paths (10 mm) through the ferrofluid.