  We investigate the potential to use a magneto-thermo-electric instability
that may be induced in a mesoscopic magnetic multi-layer (F/f/F) to create and
control magnetic superstructures. In the studied multilayer two strongly
ferromagnetic layers (F) are coupled through a weakly ferromagnetic spacer (f)
by an "exchange spring" with a temperature dependent "spring constant" that can
be varied by Joule heating caused by an electrical dc current. We show that in
the current-in-plane (CIP) configuration a distribution of the magnetization,
which is homogeneous in the direction of the current flow, is unstable in the
presence of an external magnetic field if the length L of the sample in this
direction exceeds some critical value Lc ~ 10 \mu m. This spatial instability
results in the spontaneous formation of a moving domain of magnetization
directions, the length of which can be controlled by the bias voltage in the
limit L >> Lc. Furthermore, we show that in such a situation the
current-voltage characteristics has a plateau with hysteresis loops at its ends
and demonstrate that if biased in the plateau region the studied device
functions as an exponentially precise current stabilizer.
