Liquid-metal-based magnetic fluids

Magnetic fluids, suspensions of magnetic particles in carrier liquids like water, oil or organic solvents, combine magnetic properties with fluidity to achieve features such as rapid magnetic response, reversible viscosity, and tunable thermal and optical properties. However, these carriers tend to have low densities and boiling points, affecting the suspension stability and working temperature range of magnetic fluids. Using liquid metals — which have high densities, boiling points and chemical stability in addition to excellent conductivity — as the carrier liquid can not only overcome these issues but also make the resulting liquid-metal-based magnetic fluids (LMMFs) highly conductive, substantially expanding the functions of magnetic fluids. Furthermore, LMMFs behave in complex yet versatile ways owing to synergies between the electrical conduction of the liquid metal and the magnetism of the suspended particles. This Review provides a comprehensive overview of LMMFs, beginning with their fabrication methods and an interpretation of their suspension stability. We summarize the properties and applications of LMMFs, highlighting their superiority over traditional magnetic fluids. Finally, we discuss the challenges and prospects of these materials. Liquid-metal-based magnetic fluids exhibit rich electromagnetic, thermofluidic behaviours, leading to emerging applications in soft robotics, stretchable electronics, energy management and biomedical technology. This Review covers the fabrication, properties and applications of liquid-metal-based magnetic fluids, highlighting their superiority over traditional magnetic fluids.