Wavelength dependence of the Faraday effect and magnetobirefringence in ferrofluid thin films

An enhancement of negative Faraday rotation in a dilute ferrofluid was reported near the wavelength of 0.5 μm by Yusuf. The observed phenomenon was explained in terms of a ‘‘small particle resonance.’’ The premise of the above explanation is debatable. In order to give a more detailed explanation, measurements of Faraday rotation and magnetobirefringence spectra in dense ferrofluid thin films are reported from 0.5 to 2.7 μm, and a mathematical model is derived taking into account a skew‐symmetric dielectric tensor for ferrite particles. The experiments confirm that the negative Faraday rotation is predominantly caused by the wavelength dependence of the off‐diagonal elements efxy(λ) of the dielectric tensor of the magnetic particles themselves.