Abstract
Thermomagnetic convection is driven by a temperature difference and a magnetic field
applied to a layer of fluid. Its onset is characterized by the so-called Rayleigh number Ra.
Since a temperature gradient also drives thermal diffusion in binary fluids characterized
by the Soret coefficient ST, the impact of the two transport phenomena on each other have
to be investigated with the focus on the point of transition from enhanced to hindered or
even suppressed convection. A linear stability analysis provides the functional context of
Ra(ST). Suppression of the convective motion is thereby reached for ST
-0.001 which implies a negative Soret coefficient. The zero magnetic field coefficient in ferrofluids is
positive, but measurements of the magnetic Soret coefficient in an applied magnetic field
prove that its sign is sensitive to the strength of the magnetic field. In fields higher than
75 kA/m, the Soret coefficient switches from positive to negative.
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