Remotely and selectively turning on and off the magnetization of many micro-scale magnetic actuators could be a great enabling feature in fields such as microrobotics and microfluidics. We present an array of addressable 800 × 800 × 75 μm3 micropumps made from a composite material whose net magnetic moment can be selectively turned on or off by application of a large magnetic field pulse. The material is made from a mixture of micron-scale neodymium-iron-boron and ferrite particles, and can be formed into arbitrary actuator shapes using a simple molding procedure. By selectively controlling the orientation of each of an array of micro-actuators prior to the application of the field pulse, the magnetic on/off state of each can be controlled independently. The micropumps are actuated by rotating magnetic fields up to 12 kA m−1 in strength to pump liquid through 100 μm fluid channels. A distinct transition between the on and off states is seen by application of pulsed magnetic fields of about 240 kA m−1 in strength. As a demonstration, we show addressable on/off control of two micropumps and five simple spinning magnetic microactuators, with potential applications for lab-on-a-chip type fluidic devices.
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