Electron tunnelling in planar double junctions with ferromagnetic barriers

Electron tunnelling in double junctions with ferromagnetic barriers and nonmagnetic electrodes is analysed in the sequential and coherent limit of electron tunnelling. The free-electron-like one band model is used. The tunnelling current and its spin polarisation, as well as tunnel magnetoresistance (TMR) are determined. The spin accumulation in the central electrode, leading to a nonvanishing TMR effect, is taken into account and analysed in the sequential limit. In the coherent limit the influence of resonant states on the results obtained is analysed. The conditions leading to an enhancement of TMR and negative differential resistance are discussed. The influence of the parameters of the junction on the results obtained is also investigated.