  Synthetic antiferromagnetic layers (SAF) are incorporated into spin transfer
nanopillars giving a layer composition [Co(bottom)/Ru/Co(fixed)]/Cu/Co(free),
where square brackets indicate the SAF. The Co(bottom) and Co(fixed) layers are
aligned antiparallel (AP) by strong indirect exchange coupling through the Ru
spacer. All three magnetic layers are patterned, so this AP alignment reduces
undesirable dipole fields on the Co(free) layer. Adding the Co(bottom)/Ru
layers reduces the spin polarization of the electron current passing through
the nanopillar, leading to a decreased spin-torque per unit current incident on
the Co(free) layer. This may be advantageous for device applications requiring
a reduction of the effects of a spin-torque, such as nanoscale CPP-GMR read
heads.
