Fig. 4.

Particle interaction in a rotating magnetic field. a 1–2 µm fluorescent superparamagnetic particles are dispersed within the glass slides in the absence of a magnetic field. b The superparamagnetic particles self-assemble and form spinning chains at a rotational frequency of 0.1 Hz. c The spinning chains fragment into satellites, and eventually the chain transforms into spinning orbits at a higher frequency. The rotation of the spinning aggregates is demonstrated at a rotational frequency of 20 Hz, see also Supplementary Movie 3. Scale bar, 100 µm