Controlling the Nonequilibrium Interlayer Exchange Coupling in Asymmetric Magnetic Tunnel Junctions

We predict an oscillatory bias behavior of the fieldlike spin torque, T_⊥, in magnetic tunnel junctions, which can be selectively controlled via the asymmetry in band filling between the ferromagnetic leads. This can lead to a linear or quadratic low-bias behavior, including tuning the bias-induced reversal of T_⊥. These findings reconcile the apparently contradictory experimental results recently reported in the literature. The underlying mechanism for the nonequilibrium interlayer exchange coupling (IEC) of noncollinear configurations is the interplay of four independent IEC for the majority- and minority-spin bands of the leads solely in the ferromagnetic configuration.