Magnetic field dependant backscattering of light in water based ferrofluid containing polymer covered Fe3O4 nanoparticles

We probe the effect of applied magnetic field on the backscattering light intensity from a magnetic nanofluid consisting of poly-acrylic acid coated Fe3O4 nanoparticles of diameter, similar to 15nm dispersed in water. We observe a continuous evolution of backscattered speckle pattern as a function of magnetic field strength. The speckle contrast is found to increase linearly with external magnetic field possibly due to the evolution from highly dynamic to static scatterers in the dispersion. The backscattered light intensity is found to diminish with external magnetic field, which is attributed to the delay of light propagation for the formation of standing waves within the scatterer due to the resonances in backscattered efficiency and forward-backward anisotropy factor. Interestingly, the backscattered light intensity completely recovers when magnetic field is switched off. We discuss the possible reasons for the angular variation of backscattered light intensity. Our results suggest that the field dependent light propagation through the magnetic nanofluid may find interesting applications in tunable light controlling devices. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789970]