Until now, all magnets have been made from solid materials. But what if scientists could make magnetic devices out of liquids? Researchers have managed to do exactly that. “We’ve made a new material that has all the characteristics of an ordinary magnet, but we can change its shape, and conform it to different applications because it is a liquid,” said Thomas Russell, a polymer scientist at the University of Massachusetts, Amherst, and the study’s lead author. Using a special 3D printer, Dr. Russell and his colleagues at the Lawrence Berkeley National Laboratory injected iron oxide nanoparticles into millimeter-scale droplets of toluene, a colorless liquid that does not dissolve in water. The team also added a soap-like material to the droplets, and then suspended them in water. The soap-like material caused the iron oxide nanoparticles to crowd together on the surface of the droplets and form a semisolid shell. “The particles get stuck in place, like a traffic jam at 5 o’clock,” Dr. Russell said. Next, the scientists placed the droplets on a stirring plate with a spinning bar magnet, and observed something extraordinary: The solid magnet caused the positive and negative poles of the liquid magnets to follow the external magnetic field, making the droplets dance on the plate. When the solid magnet was removed, the droplets remained magnetized. The droplets created by Dr. Russell and his team become magnetic and stay that way, thanks to the nanoparticle shell that forms within the soapy emulsion.