  We present a theory of magnetotransport through an electronic orbital, where
the electron spin interacts with a (sufficiently) large external spin via an
exchange interaction. Using a semiclassical approximation, we derive a set of
equations of motions for the electron density matrix and the mean value of the
external spin that turns out to be highly nonlinear. The dissipation via the
electronic leads is implemented in terms of a quantum master equation that is
combined with the nonlinear terms of the spin-spin interaction. With an
anisotropic exchange coupling a variety of dynamics is generated, such as
self-sustained oscillations with parametric resonances or even chaotic
behavior. Within our theory we can integrate a Maxwell-demon-like closed-loop
feedback scheme that is capable of transporting particles against an applied
bias voltage and that can be used to implement a spin filter to generate
spin-dependent oscillating currents of opposite directions.

Mesoscale and Nanoscale Physics