  Thermal ratchets can extract useful work from random fluctuations. This is
common in the molecular scale, such as motor proteins, and has also been used
to achieve directional transport in microfluidic devices. In this work, we use
the ratchet principle to induce net motility in an externally powered magnetic
colloid, which otherwise shows reciprocal (back and forth) motion. The
experimental system is based on ferromagnetic micro helices driven by
oscillating magnetic fields, where the reciprocal symmetry is broken through
asymmetric actuation timescales. The swimmers show net motility with an
enhanced diffusivity, in agreement with the numerical calculations. This new
class of microscale, magnetically powered, active colloids can provide a
promising experimental platform to simulate diverse active matter phenomena in
the natural world.
