Theory of Spin Torque Switching Current for the Double Magnetic Tunnel Junction

A single-domain model for spin-transfer torque switching of double magnetic tunnel junctions with perpendicularly magnetized layers is developed. An analytical formula is derived for the switching current threshold, Ic0. Surprisingly, the model predicts that the switching current can be reduced by a factor of 10 compared to single magnetic tunnel junctions, for sufficiently large spin-polarizations. This effect is explained in terms of the "enhanced antiparallel-to-parallel" spin torque, familiar from single magnetic tunnel junctions.