  We study the spin and charge dynamics of electrons in n-doped II--VI
semiconductor multiple quantum wells when one or more quantum wells are doped
with Mn. The interplay between strongly nonlinear inter-well charge transport
and the large tunable spin-splitting induced by exchange interactions with
spin-polarized Mn ions produces interesting new spin dependent features. The
tunneling current between quantum wells can be strongly spin polarized and,
under certain conditions, can develop self sustained oscillations under a
finite dc voltage. The spin polarization oscillates in both magnetic and
nonmagnetic quantum wells and the time average in magnetic wells can differ
from its zero-voltage value. Our numerical simulations demonstrate that the
amplitude of the spin polarization oscillations depends on the distribution of
magnetic wells within the sample. We discuss how the spin polarized current and
the spin polarization of the quantum wells can be tailored experimentally.
