  Spin-dependent transport through an interacting single-level quantum dot
coupled to ferromagnetic leads with non-collinear magnetizations is analyzed
theoretically. The transport properties and average spin of the dot are
investigated within the nonequilibrium Green function technique based on the
equation of motion in the Hartree-Fock approximation. Numerical results show
that Coulomb correlations on the dot and strong spin polarization of the leads
significantly enhance precession of the average dot spin around the effective
molecular field created by the external electrodes. Moreover, they also show
that spin precession may lead to negative differential conductance in the
voltage range between the two relevant threshold voltages. Nonmonotonous
angular variation of electric current and change in sign of the tunnel
magnetoresistance are also found. It is also shown that the diode-like behavior
in asymmetrical junctions with one electrode being half-metallic is
significantly reduced in noncollinear configurations.
