  In this manuscript we describe the realization of a minimal hybrid
microswimmer, composed of a ferromagnetic nanorod and a paramagnetic
microsphere. The unbounded pair is propelled in water upon application of a
swinging magnetic field that induces a periodic relative movement of the two
composing elements, where the nanorod rotates and slides on the surface of the
paramagnetic sphere. When taken together, the processes of rotation and sliding
describe a finite area in the parameter space, which increases with the
frequency of the applied field. We develop a theoretical approach and combine
it with numerical simulations, which allow us to understand the dynamics of the
propeller and explain the experimental observations. Furthermore, we
demonstrate a reversal of the microswimmer velocity by varying the length of
the nanorod, as predicted by the model. Finally, we determine theoretically and
in experiments the Lighthill's energetic efficiency of this minimal magnetic
microswimmer.
