Nano Ferrofluid

Ferrofluid is a liquid which becomes strongly magnetized in the presence of a magnetic field.
Ferrofluids are colloidal mixtures composed of nanoscale ferromagnetic, or ferrimagnetic, particles suspended in a carrier fluid, usually an organic solvent or water. The ferromagnetic nanoparticles are coated with a surfactant to prevent their agglomeration.
NASA has experimented using ferrofluids in a closed loop as the basis for a spacecraft.