  Spin-dependent transport through a two-level quantum dot in the sequential
tunneling regime is analyzed theoretically by means of a real-time diagrammatic
technique. It is shown that the current, tunnel magnetoresistance, and shot
noise (Fano factor) strongly depend on the transport regime, providing a
detailed information on the electronic structure of quantum dots and their
coupling to external leads. When the dot is asymmetrically coupled to the
leads, a negative differential conductance may occur in certain bias regions,
which is associated with a super-Poissonian shot noise. In the case of a
quantum dot coupled to one half-metallic and one nonmagnetic lead, one finds
characteristic Pauli spin blockade effects. Transport may be also suppressed
when the dot levels are coupled to the leads with different coupling strengths.
The influence of an external magnetic field on transport properties is also
discussed.
