Computational assessment of possible origins of the back-hopping effect in magnetic tunnel junctions

In this work we employ macrospin simulations of the magnetization dynamics obtained from the Landau-Lifshitz-Gilbert equation coupled to angular momentum transport yielded by the nonequilibrium Green's function formalism to investigate two possible origins of the back-hopping effect in magnetic tunnel junctions with one layer of a synthetic antiferromagnet as reference layer. One possible origin discussed in this work is an additional sign reversal of the dampinglike (parallel) torque component as a function of the applied voltage. The other is the destabilization and switching of the reference layer by the spin-transfer torque. We find that this destabilization gives rise to a dynamic behavior manifesting in a back-and-forth switching of the free layer, while the sign reversal of the dampinglike torque results in a second hysteresis loop.