First-ever ferromagnetic liquid surprises researchers

Permanent magnets made of small droplets of liquid have been created and studied by scientists in the US and China. The researchers believe that these are the first-ever liquid permanent magnets to be made. The shapes of the magnetized droplets can be changed, and this could lead to practical applications such as actuators for tiny soft robots.

Many materials have magnetic moments that line up when exposed to an external magnetic field. In a ferromagnetic material (a permanent magnet), coupling between moments ensures that the material remains magnetic after the field has been removed. In other materials called paramagnets, thermal fluctuations quickly overcome the coupling once the external field has been removed and the material ceases to be magnetic.

Ferrofluids are paramagnets that consist of magnetic nanoparticles dispersed in a liquid. When exposed to a magnetic field, the combined effects of gravity, surface tension and the magnetic attraction between nanoparticles can create unusual spiky structures on the surfaces of ferrofluids. However, when the magnetic field is removed, ferrofluids return to a normal liquid state.

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