Controlling the rotation modes of hematite nanospindles using dynamic magnetic fields.

The magnetic field-induced actuation of colloidal nanoparticles has enabled tremendous recent progress towards microrobots, suitable for a variety of applications including targeted drug delivery, environmental remediation, or minimally invasive surgery. Further size reduction to the nanoscale requires enhanced control of orientation and locomotion to overcome dominating viscous properties. Here, control of the coherent precession of hematite spindles a dynamic magnetic field is demonstrated using nanoscale particles. Time-resolved small-angle scattering and optical transmission measurements reveal a clear frequency-dependent variation of orientation and rotation of an entire ensemble of non-interacting hematite nanospindles. The different motion mechanisms by nanoscale spindles in bulk dispersion resemble modes that have been observed for much larger, micron-sized elongated particles near surfaces. The dynamic rotation modes promise hematite nanospindles as a suitable model system for field-induced locomotion in nanoscale magnetic robots.