Orientations of overdamped magnetic nanorod-gyroscopes

Overdamped magnetic nanorod-gyroscopes driven by a rotating magnetic field undergo a series of reorientations when sedimenting on top of a surface in a viscous liquid. By changing the amplitude and the rotation frequency of the driving magnetic field, the nanorod-gyroscope either synchronizes or desynchronizes with the field and rotates either around its long or short axis. The different regimes of motion are explained theoretically by coupling the nanorod-gyroscopes motion to the creeping flow equations of the surrounding fluid. It is shown that friction anisotropy plays an important role for the orientation of the nanorod-gyroscopes.