Spin-polarized transport in structures with tunnel barriers

We study spin-dependent transport theoretically in structures with a barrier composed of magnesium oxide and ferromagnetic electrodes with a noncollinear orientation of magnetizations in the ferromagnetic layers. We consider the effects of tunnel magnetoresistance and of the spin torque in the two-band s–d model using the Keldysh technique of nonequilibrium Green's functions with the s–d hybridization taken into account. We investigate the role of a chromium layer as an additional spin filter for s electrons and the possibility of increasing the effects of tunnel magnetoresistance and of the spin torque for the resonance tunneling in the five-layer structure Fe|Cr|Fe|MgO|Fe.