  We investigate transport through a single-level quantum dot coupled to
noncollinearly magnetized ferromagnets in the presence of localized spins in
either the tunnel barrier or on the quantum dot. For a spin embedded in the
tunnel barrier, we find an interplay between current-induced switching of the
spin, spin-dependent tunneling through the barrier and spin accumulation on the
dot resulting in characteristic signals in the current. We, furthermore, find
huge Fano factors due to random telegraph noise. For noncollinear geometries,
an exchange field that depends on the impurity spin state leads to
characteristic fingerprints in the transport properties. In the case of a spin
on the quantum dot, we find that the frequency-dependent Fano factor can be
used to study the nontrivial dynamics of the spins on the dot due to the
interplay between exchange interaction and coupling to external and exchange
magnetic fields.

Mesoscale and Nanoscale Physics