Controlling the rotation modes of hematite nanospindles by 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 we demonstrate how the coherent precession of nanoscale hematite spindles can be controlled via dynamic magnetic fields. Using time-resolved Small-Angle Scattering and optical transmission measurements, we reveal a clear frequency-dependent variation of orientation and rotation of an entire ensemble of hematite nanospindles. Our findings are in line with the different motion mechanisms observed for much larger, micron sized elongated particles near surfaces. The different dynamic rotation modes promise hematite nanospindles as a suitable model system towards field-induced locomotion in nanoscale magnetic robots.