Thermodiffusion in ferrofluids regarding thermomagnetic convection

Magnetic fluids, also called ferrofluids, are binary liquids consisting of magnetic nanoparticles being dispersed in a carrier liquid. They show very strong thermodiffusive behaviour with a Soret coefficient (S-T) of approximately 0.16 K-1 without a magnetic field. The dependence of the Soret coefficient on a magnetic field can lead to even higher values, and to a change in the coefficient's sign. This change in the direction of movement of the nanoparticles strongly affects the onset of thermomagnetic convection. A linear stability analysis reveals that thermodiffusion with a positive sign of the Soret coefficient enhances the onset of convection, whereas negative coefficients starting at about -0.001 K-1 suppress convection at all. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.