  It is well-known that the Curie temperature, and hence the magnetization, in
diluted magnetic semiconductor (DMS) like Ga$_{1-x}$Mn$_x$As can be controlled
by changing the equilibrium density of holes in the material. Here, we propose
that even with a constant hole density, large changes in the magnetization can
be obtained with a relatively small imbalance in the quasi-Fermi levels for
up-spin and down-spin electrons. We show, by coupling mean field theory of
diluted magnetic semiconductor ferromagnetism with master equations governing
the Mn spin-dynamics, that a mere splitting of the up-spin and down-spin
quasi-Fermi levels by 0.1 meV will produce the effect of an external magnetic
field as large as 1 T as long as the alternative relaxation paths for Mn spins
(i.e. spin-lattice relaxation) can be neglected. The physics is similar to the
classic Overhauser effect, also called the dynamic nuclear polarization, with
the Mn impurities playing the role of the nucleus. We propose that a lateral
spin-valve structure in anti-parallel configuration with a DMS as the channel
can be used to demonstrate this effect as quasi-Fermi level splitting of such
magnitude, inside the channel of similar systems, have already been
experimentally demonstrated to produce polarization of paramagnetic impurity
spins.
