Autonomous
swimmers have been intensively studied in recent years
due to their numerous potential applications in many areas ranging
from biomedicine to environmental remediation. Their motion is based
either on different self-propulsion mechanisms or on the use of various
external stimuli. Herein, the synergy between the ion flux around
self-electrophoretic Mg/Pt Janus swimmers and an external magnetic
field is proposed as an efficient alternative mechanism to power swimmers
on the basis of the resulting Lorentz force. A strong magnetohydrodynamic
effect is observed due to the orthogonal combination of magnetic field
and spontaneous ionic currents, leading to an increase of the swimmer
speed by up to 2 orders of magnitude. Furthermore, the trajectory
of the self-propelled swimmers can be controlled by the orientation
of the magnetic field, due to the presence of an additional torque
force caused by a horizontal cation flux along the swimmer edges,
resulting in predictable clockwise or anticlockwise motion. In addition,
this effect is independent of the swimmer size, since a similar type
of rotational motion is observed for macro- and microscale objects.