Transmitted Light Intensity and the Speckle Pattern in a Poly-Acrylic Acid Stabilized Ferrofluid in the Presence of an External Magnetic Field

We study the propagation of light through a disordered magnetic colloidal media-a water based poly-acrylic acid stabilized Fe3O4 nanoparticles based ferrofluid. The behavior of the transmitted light intensity and the speckle pattern in presence of an external magnetic field perpendicular to the direction of propagation of the incident light is studied. The transmitted light intensity and the speckle parameters such as speckle size, intensity, contrast, polarization, coherence and intensity correlations coefficient etc. are found to be strongly influenced by the external magnetic field. The resonances in the total extinction efficiency and the forward anisotropy factor due to the changes in the dimension of the scatterers due to dipolar interactions and the changes in the surface roughness of the field induced aggregates are considered to contribute to the variations in the transmitted light intensity and the speckle parameters. The speckle contrast is found to increase with external magnetic field, which indicates a transformation of 'dynamic' to 'fully developed' speckle pattern due to the formation of chain-like structure in water. The transmitted light speckle correlation coefficient shows a power law decay with external magnetic field that confirms the fractal nature of the aggregates in dispersion. These magneto-optical properties of magnetic nanofluid offer potential applications in various 'Opto-fluidic Gadgets.'