FIG. 4.
Optical images of three different phase regimes of a 2.8-μm diameter bead moving around a 10-μm diameter micro-magnet disk exposed to a Happ = 2 mT in-plane rotating magnetic field. Red arrows represent the instantaneous phase angle of the external field. For panels (a)–(d), the bead is phase-locked with the external field at a driving frequency of 0.8 Hz. In panels (e)–(h), the bead undergoes phase-slipping motion at a driving frequency of 1.2 Hz. In panels (i)–(l), the bead is in a phase-insulated state at a driving frequency of 20 Hz. (Multimedia view) [URL: http://dx.doi.org/10.1063/1.4936219.2]Download video file (1.1MB, mp4) DOI: 10.1063/1.4936219.2)