Ab initio studies of the spin-transfer torque in magnetic tunnel junctions.
We calculate the spin-transfer torque in Fe/MgO/Fe tunnel junctions and compare the results with those for all-metallic junctions. The spin-transfer torque is interfacial due to the half-metallic nature of the Fe Delta1 states. For samples with typical interfacial roughness, the in-plane torque varies linearly with bias and the out-of-plane torque varies quadratically, both in quantitative agreement with experiment. For ideal samples, we predict that the out-of-plane component of the torque varies linearly with bias and oscillates as a function of the ferromagnetic layer thickness.