Synthesis and study of γ-Fe2O3 and CoFe2O4 based ferrofluids by means of spectroscopic Mueller matrix ellipsometry

Ferrofluids are colloidal suspensions generally composed of ferromagnetic or ferrimagnetic nanoparticles (NPs). In the present study, the authors have focused on the ellipsometric characterization of two types of ferrofluids: one constituting maghemite (gamma-Fe2O3) NPs and the other cobalt ferrite (CoFe2O4) NPs. The optical properties of the NPs are extracted from the ellipsometric spectra by using the Maxwell-Garnett effective medium approximations. As expected, Mueller matrix measurements reveal that the ferrofluid becomes anisotropic under the influence of a magnetic field. The authors correlate this anisotropy to the preferential orientation of NPs along the magnetic field. Published by the AVS.