  The interplay of tunneling transport and carrier-mediated ferromagnetism in
narrow semiconductor multi-quantum well structures containing layers of GaMnAs
is investigated within a self-consistent Green's function approach, accounting
for disorder in the Mn--doped regions and unwanted spin-flips at
heterointerfaces on phenomenological ground. We find that the magnetization in
GaMnAs layers can be controlled by an external electric bias. The underlying
mechanism is identified as spin-selective hole tunneling in and out of the
Mn-doped quantum wells, whereby the applied bias determines both hole
population and spin polarization in these layers. In particular we predict
that, near resonance, ferromagnetic order in the Mn doped quantum wells is
destroyed. The interplay of both magnetic and transport properties combined
with structural design potentially leads to several interrelated physical
phenomena, such as dynamic spin filtering, electrical control of magnetization
in individual magnetic layers, and, under specific bias conditions, to
self-sustained current and magnetization oscillations
(magneticmulti-stability). Relevance to recent experimental results is
discussed.
