Influence of Band Parameters on Spin-Transfer Torque in Tunnel Junctions: Model Calculations

We study the in-plane spin-transfer torque in magnetic tunnel junctions for different band fillings and exchange splittings. The bias range over which the in-plane torque is linear depends strongly on these parameters. If the ferromagnetic layer is half-metallic with respect to the tunneling states, the linear bias range for the in-plane torque is significantly larger than if the behavior is metallic. For parameters that reproduce the important features of the Fe band structure, the results are in agreement with experimental data as well as with ab initio calculations.