Magnetic field induced optical variation in nanosize iron oxide fluid-particles

The transmission of light through magnetic fluid containing the magnetic nanoparticles with diameters of 7, 9 and 12 nm have been investigated as a function of particle size and thickness of the films with wavelength between 400 and 750 nm, and applied magnetic fields up to 275 Oe. It was found that the transmittance decreased with the increasing particle size as well as film thickness. The transmittance increases with increasing wavelength and saturates at 700 nm at film thickness of 10 μm for all samples. The onset of transmittance shifts to higher wavelength with increasing film thickness. For a given film thickness, the transmittance increases with increasing magnetic field for films with particle size of 7 and 9 nm, but decreases in the particle size of 12 nm. Moreover, under a given magnetic field, the transmittance decreases exponentially with the increasing film thickness. The ordered structures of the magnetic columns were formed in the magnetic fluid films under the influence of the external magnetic field. These ordered structures are responsible for the significant field dependent on observed transmittance. The transmittance of the samples is inverse proportional to the area covered by the droplets of the magnetic fluid.