We report magnetoresistance, focused Kerr effect, and Lorentz microscopy experiments performed on a nanoscale Permalloy bridge connecting microscale pads. These pads can be switched from a parallel to antiparallel state through the application of small fields, causing a detectable magnetoresistance. We show that this switching field Hsw is modified by the application of a high current density (Jdc) through spin-transfer torque effects, caused by the spin-current interacting with the magnetization gradients generated by the device geometry, yielding an estimate for the spin-transfer torque efficiency ξ=dHsw/dJdc=0.027 ± 0.001 Oe/MA cm-2.
Hickey, M. C., Ngo, D. -T., Lepadatu, S., Atkinson, D., McGrouther, D., McVitie, S., & Marrows, C. H. (2010). Spin-transfer torque efficiency measured using a Permalloy nanobridge. Applied Physics Letters, 97(20), 202505. https://doi.org/10.1063/1.3520144