Electron transport through nanoscopic spin valves

Spin-polarized transport through a quantum dot strongly coupled to ferromagnetic electrodes with non-collinear magnetic moments is analyzed theoretically in terms of the non-equilibrium Green's function formalism. The influence of an effective exchange field (due to coupling with ferromagnetic electrodes) on tunneling current, linear and non-linear conductance, and tunnel magnetoresistance is studied in detail. In non-collinear configurations we find negative differential conductance for sufficiently large bias voltage. Negative differential conductance can also occur in parallel configurations, when the bare dot level is located well above the Fermi level. Apart from this, a non-monotonic behavior of electric current with increasing angle between magnetic moments of the electrodes is found in systems with the bare dot level located close to the Fermi level.