Thermomagnetic convection

Ferrofluids can be used to transfer heat, since heat and mass transport in such magnetic fluids can be controlled using an external magnetic field. B. A. Finlayson first explained in 1970 (in his paper "Convective instability of ferromagnetic fluids", Journal of Fluid Mechanics, 40:753-767) how an external magnetic field imposed on a ferrofluid with varying magnetic susceptibility, e.g., due to a temperature gradient, results in a nonuniform magnetic body force, which leads to thermomagnetic convection.

Source: Wikipedia — Thermomagnetic convection (CC BY-SA 4.0)