Magnetically modulated optical transmission of magnetic fluid films

The optical transmission of the magnetic fluid film under perpendicular magnetic fields was investigated by measuring the transmitted intensity of the normally incident light through the film. The transmittance I/I₀ of the magnetic fluid film was observed to decrease with the increase of the magnetic field strength H due to the reduction in the area occupied by the relatively optic transparent liquid phase. Moreover, under a given H, the transmittance decreased exponentially with the increasing film thickness L, i.e. I/I₀=exp(-L/δ), where the δ denotes the attenuation distance. It was further found that the δ varies with the magnetic field strength and the concentration of the fluid, but is independent of the sweep rate of the field.