  Locomotion via cyclic moves presents a challenge to mesoscopic objects in
overdamped environments, where time reversibility may prevent directed motion.
Most reported cyclic movers exploit anisotropic drag to push themselves
forward. Under an oscillating drive, however, anisotropic drag enables
locomotion only if the objects can change their shape. Here, we present a
strategy that unexpectedly enables structurally invariant objects to move under
oscillating fields. The objects are self-assembled clusters of magnetic
particles that exhibit an off-centered dipole moment. By theoretical modeling
and in experiments with magnetic Janus particles, we demonstrate that the
interaction between such anisotropic particles in the cluster breaks time
reversibility. Experimentally, we show that the magnetic configuration of a
cluster determines its motion path. We realize stirrers and steerable movers
with helical or directed path using the same particle system. The presented
strategy based on internal interactions establishes a counterpart to locomotion
via anisotropic drag.
