Research Papers in Physics and Astronomy


Date of this Version


Document Type



Published in Science 365, 264–267 (19 July 2019).

DOI: 10.1126/science.aaw8719


Copyright © 2019 by the Authors; exclusive licensee American Association for the Advancement of Science. Used by permission.


Solid ferromagnetic materials are rigid in shape and cannot be reconfigured. Ferrofluids, although reconfigurable, are paramagnetic at room temperature and lose their magnetization when the applied magnetic field is removed. Here, we show a reversible paramagnetic-to-ferromagnetic transformation of ferrofluid droplets by the jamming of a monolayer of magnetic nanoparticles assembled at the water-oil interface. These ferromagnetic liquid droplets exhibit a finite coercivity and remanent magnetization. They can be easily reconfigured into different shapes while preserving themagnetic properties of solid ferromagnets with classic north-south dipole interactions. Their translational and rotational motions can be actuated remotely and precisely by an external magnetic field, inspiring studies on active matter, energy-dissipative assemblies, and programmable liquid constructs.

Includes supplementary text and figures; supplemental movies attached below.