The familiar picture one associates with electromagnets is their use at a scrap yard for lifting compacted vehicles. The ability to move much smaller magnetic particles with a magnetic field may find a host of applications. For instance, the mechanical properties of cell walls have been probed by gently tugging on an implanted magnetic particle.
By scaling the system down, Barbic et al. manipulated magnetic particles of a few micrometers (μm) in size. Their magnetic manipulator consists of a soft ferromagnetic core 50 μm in diameter, sharpened to a point and wound by a 25 μm-diameter copper wire. The authors estimate that the tip can exert a force of 0.5 piconewtons for a 10-milliampere current passed through the coil wires, and they suggest that the negligible heating of the sample offers an advantage over optical trapping techniques. — ISO
Appl. Phys. Lett. 79, 1897 (2001).