A Capillary-Locking Strategy for Programming Magnetic Domains in Soft Materials

Magnetic soft materials derive their programmable shape morphing from spatially encoded magnetic anisotropy, which typically requires the controlled reorientation of magnetic particles during fabrication. Magnetic fluids or suspensions, in which magnetic particles possess high rotational freedom, offer a promising platform for constructing and programming such materials. However, the intrinsic fluidity of magnetic suspensions also leads to severe magnetofluidic instabilities, preventing precise magnetic programming. Here, we introduce capillary locking as a general physical strategy to stabilize magnetic fluids in open systems. By infiltrating a magnetic polymer solution containing hard-magnetic microparticles into an interconnected porous scaffold, capillary forces at solid–liquid–air interfaces immobilize the fluid while preserving the rotational freedom of the magnetic particles. This interfacial confinement suppresses magnetically induced flow and surface instabilities without encapsulation, enabling stable magnetic domain programming under weak magnetic fields. The capillary locked magnetic phase can be reversibly liquefied and resolidified through solvent exchange, allowing repeated reprogramming and fabrication of flexible magnetic composites with programmable magneto-mechanical responses. Owing to the open porous architecture, the system further supports solvent-assisted processing, modular assembly, and material recycling. These results establish capillary locking as a universal route for constructing reprogrammable magnetic soft materials from inherently unstable magnetic fluids.