Spin transfer torque in double barrier magnetic tunnel junctions

We present tight-binding calculations of the current-induced spin torque in double-barrier magnetic tunnel junctions (DBMTJ) using the non-equilibrium Keldysh formalism. The components of the local spin torque in the central ferromagnetic region, parallel, Tprallel, and perpendicular, Tperpendicular, to the interface are strongly enhanced for certain thickness of the middle layer. The underlying mechanism for the spin torque enhancement is the relative position of the majority and minority quantum well states within the bias energy window around the Fermi level. Both Tprallel and Tperpendicular exhibit oscillatory behavior in the middle FM region