LIGHT SCATTERING BEHAVIOR OF MAGNETIC FIELD INDUCED DIRECTIONAL SELF ASSEMBLY OF IRON OXIDE NANOPARTICLE SUSPENSION

Abstract

The magnetic control on scattering of light by ultrafine iron oxide (γ- Fe2O3 ) nanoparticles suspended in a carrier liquid was investigated. The light scattering behavior was studied using laser light under the influence of a permanent magnet over a rotating frame of reference. When the magnet is rotated continuously from 0° to 360° with respect to the direction of the incident laser beam, the scattered light pattern from the sample has the same angular displacement but in counter direction to the magnetic field rotation. When external field is not applied to the ferrofluid, no other preferred directional scattering of light is observed. The applied magnetic field induces directional self assembly of magnetic nanoparticles through dipole–dipole interactions. This finally leads to the formation of "nanoparticle grating" and the optical geometry of diffraction grating clearly describes the anomalous scattering behavior of the ferrofluid. Most interestingly, for each complete orientation of the field from 0° to 360°, the transmitted light intensity switches between maxima and minima for longitudinal and transverse applied magnetic fields.