Crucial role of interfacial alloying on spin-transfer torque in magnetic tunnel junctions

We demonstrate that interfacial disorder in magnetic tunnel junctions (MTJs) has a dramatic effect on the bias behavior of both spin-transfer and field-like spin torques, leading to strong enhancement, sign reversal, and bias asymmetry. The underlying mechanism lies on the impurity-induced resonance energies, which can be selectively controlled with alloying and/or bias. The predictions explain for the first time the experimental results in "dirty" junctions and have important implications on exploiting further the alloying effect to optimize the current-induced magnetization switching.