  A paradigmatic microswimmer is the three-linked-spheres model, which follows
a minimalist approach for propulsion by shape shifting. As such, it has been
the subject of numerous analytical and numerical studies. In this Rapid
Communication, an experimental three-linked-spheres swimmer is created by
self-assembling ferromagnetic particles at an air-water interface. It is
powered by a uniform oscillating magnetic field. A model, using two harmonic
oscillators, reproduces the experimental findings. Because the model remains
general, the same approach could be used to design a variety of efficient
microswimmers.
