Magnetic field induced optical transmission study in an iron nanoparticle ferrofluid

Optical transmission of an iron nanoparticle ferrofluid has been investigated as a function of incident optical wavelengths between 450 and 700 nm and applied magnetic fields up to 200 Oe. The transmittance decreases as the thickness and concentration of the Fe ferrofluid films increase. This effect is more manifest with shorter incident wavelength. The decrease of transmittance for sample prepared by electrochemical method is much more rapidly than that of samples prepared by laser ablation technique. However, the magnetic field effect for these samples is vise versa. The aspect ratio of the Fe nanoparticles we prepared is roughly between 1 and 2. The decrease of the transmittance between 575 and 450 nm is explained by a classical electrostatic calculation based on the Mie/Drude formalism.