Effective exchange interaction in tunnelling junctions based on a quantum dot with non-collinear magnetic moments of the leads

Electron tunnelling through a spin-split discrete level of an interacting quantum dot coupled to two ferromagnetic electrodes (leads) is investigated theoretically in the sequential-tunnelling regime. Spinsplitting of the dot level is induced by an effective exchange interaction between the spin on the dot and spins in the leads. The calculations apply to arbitrary angles enclosed between the magnetizations of the external electrodes. It is shown that the interplay between effective exchange field and Coulomb correlations on the dot may enhance the tunnel magnetoresistance at certain bias voltages. It is also found that a large spin splitting appearing for strong Coulomb correlations gives rise to an enhanced diode-like effect. Finally, it is shown that by rotating the magnetization of one of the electrodes, one can modulate the amplitude of the spin-polarized current, from a blockade in the parallel or antiparallel configuration to its maximum value in the non-collinear case.