Temperature dependent light transmission in ferrofluids

We investigate the influence of temperature on the magnetic field induced light transmission in a kerosene based ferrofluid containing oleic acid coated Fe3O4 nanoparticles, where the direction of propagation of light is parallel to the direction of the external magnetic field. At a fixed temperature the transmitted light intensity is found to monotonically increase with incident wavelength due to reduced extinction efficiency at higher wavelength. The transmitted intensity decreases with external magnetic field due to enhanced scattering from the field induced linear chain like structures along the direction of the external magnetic field and due to the build-up of standing waves inside the scattering medium. The extinction of the field induced transmitted light intensity is found to occur at a lower external field as the sample temperature is lowered. The rate of extinction of normalized transmitted light intensity decreased linearly with increasing sample temperature due to slower field induced aggregation kinetics because of an increased Brownian motion of the suspended nanoparticles and a reduced coupling constant. The observed temperature dependent magneto-optical properties of magnetic nanofluids can be exploited for applications in optical devices.