The rules about what makes a good magnet may not be as rigid as scientists thought. Using a mixture containing magnetic nanoparticles, researchers have now created liquid droplets that behave like tiny bar magnets.

Magnets that generate persistent magnetic fields typically are composed of solids like iron, where the magnetic poles of densely packed atoms are all locked in the same direction (SN: 2/17/18, p. 18). While some liquids containing magnetic particles can become magnetized when placed in a magnetic field, the magnetic orientations of those free-floating particles tend to get jumbled when the field goes away — causing the liquid to lose its magnetism.

Now, adding certain polymers to their recipe has allowed researchers to concoct permanently magnetized liquid droplets. These tiny, moldable magnets, described in the July 19 Science, could be used to build soft robots or capsules that can be magnetically steered through the body to deliver drugs to specific cells.