Resonant spin-torque in double barrier magnetic tunnel junctions

Spin-torque effects were investigated in double barrier magnetic tunnel junctions of the form F1/I1/F/I2/F2 where F is a soft ferromagnetic layer, I1 and I2 are two tunnel barriers, and F1 and F2 are two ferromagnetic layers whose magnetization are pinned in-plane, in either antiparallel or parallel magnetic configuration. We show that for some particular thickness of the F layer, resonant effects take place in the F layer, which enhance the net spin-torque amplitude by more than an order of magnitude. The spin-torque was calculated as a function of distance from the barriers within the F layer. It has an oscillatory behavior with very large amplitude when the resonance conditions are fulfilled.