Microscopic magnetic rollers have been caught moving the 'wrong' way, rolling against the direction they are being pushed.
April 14, 2026
Original Paper
Regular and Anomalous Motion of Individual Magnetic Quincke Rollers Under Rotating Magnetic Field
arXiv · 2604.11132
The Takeaway
Scientists observed particles that roll counter-clockwise even though they are being driven by a clockwise magnetic field. This 'anomalous' motion reveals a complex tug-of-war between liquid friction and magnetism that could be used to steer tiny robots inside the body.
From the abstract
We report the motion of individual magnetic Quincke rollers composed of silica particles doped with superparamagnetic iron oxide nanoparticles, whose activity arises from the coupling between Quincke rolling and an externally applied rotating magnetic field. We applied a clockwise (CW) rotating magnetic field of magnitude approximately 11 mT and rotational frequencies ranging from 0.2 to 2.75 Hz. At low frequencies, the dominant mode of motion is a CW helical trajectory. Circular trajectories em