  We have obtained microscopic evidence of the influence of domain wall stray
fields on the nanosecond magnetization switching in magnetic trilayer systems.
The nucleation barrier initiating the magnetic switching of the soft magnetic
Fe20Ni80 layer in magnetic tunnel junction-like FeNi/Al2O3/Co trilayers is
considerably lowered by stray fields generated by domain walls present in the
hard magnetic Co layer. This internal bias field can significantly increase the
local switching speed of the soft layer. The effect is visualized using
nanosecond time- and layer-resolved magnetic domain imaging and confirmed by
micromagnetic simulations.
