  We present a Non-Equilibrium Green's Function based model for spin torque
transfer (STT) devices which provides quantitative agreement with
experimentally measured (1) differential resistances, (2) Magnetoresistance
(MR), (3) In-plane torque and (4) out-of-plane torque over a range of bias
voltages, using a single set of three adjustable parameters. We believe this is
the first theoretical model that is able to cover this diverse range of
experiments and a key aspect of our model is the inclusion of multiple
transverse modes. We also provide a simple explanation for the asymmetric bias
dependence of the in-plane torque, based on the polarization of the two
contacts in energy range of transport.
