Brownian motion allows microscopically dispersed nanoparticles to be stable in ferrofluids, as well as causes magnetization relaxation and prohibits permanent magnetism. Here we decoupled the particle Brownian motion from colloidal stability to achieve a permanent fluidic magnet with high magnetization, flowability and reconfigurability. The key to create such permanent fluidic magnets is to maintain a stable magnetic colloidal fluid by using non-Brownian magnetic particles to self-assemble a three-dimensional oriented and ramified magnetic network structure in the carrier fluid. This structure has high coercivity and permanent magnetization, with long-term magnetization stability. We establish a scaling theory model to decipher the permanent fluid magnet formation criteria and formulate a general assembly guideline. Further, we develop injectable and retrievable permanent-fluidic-magnet-based liquid bioelectronics for highly sensitive, self-powered wireless cardiovascular monitoring. Overall, our findings highlight the potential of permanent fluidic magnets as an ultrasoft material for liquid devices and systems, from bioelectronics to robotics.

布朗运动使微观分散的纳米颗粒在铁磁流体中保持稳定，并引起磁化弛豫并阻止永磁。在这里，我们将粒子布朗运动与胶体稳定性解耦，以获得具有高磁化、流动性和可重构性的永久流体磁体。制造这种永久流体磁体的关键是通过使用非布朗磁性颗粒在载液中自组装三维定向和分支的磁网络结构来保持稳定的磁性胶体流体。这种结构具有高矫顽力和永磁化强度，具有长期磁化稳定性。我们建立了一个缩放理论模型来解读永磁体形成标准并制定通用组装指南。此外，我们还开发了可注射和可回收的基于永磁体的液体生物电子学，用于高灵敏度、自供电无线心血管监测。总的来说，我们的研究结果强调了永磁体作为超软材料用于液体设备和系统（从生物电子学到机器人）的潜力。