| Theoretical analysis of electronic transport through a two-barrier magnetic tunnel junction based on a single-level interacting quantum dot (QD) is carried out. The key point of our considerations is diode-like behavior of transport characteristics of an asymmetric tunnel junction with one electrode being half-metallic. A number of mechanisms leading to modifications of the diode-like behavior have been discussed by means of the nonequilibrium Green-function technique. It is found that the diode effect is reduced for a nonmagnetic QD coupled to external ferromagnetic electrodes with noncollinear magnetic moments, whereas it is significantly enhanced for a magnetic QD in the antiparallel configuration. By taking into account spin-flip processes in the barriers, some suppression of the diode effect is found for a wide range of transport voltages. Finally, interaction of the quantum dot with a phonon field has been included in the theoretical description. It is shown that the electron-phonon interaction gives rise to oscillations of the tunnel magnetoresistance. In asymmetrical junctions, the electron-phonon coupling may lead to a significant suppression or enhancement of the tunneling current, depending on the bias polarization. |
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