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Journal: PRB

Authors: M. R. Hajiali,1 M. Hamdi,2 S. E. Roozmeh,1 and S. M. Mohseni2,*

Abstract: We study the ac current-driven domain wall motion in bilayer ferromagnetic metal (FM)/nonmagnetic metal
(NM) nanowires. The solution of the modified Landau-Lifshitz-Gilbert equation including all the spin transfer
torques is used to describe motion of the domain wall in the presence of the spin Hall effect. We show that the
domain wall center has a second-harmonic frequency response in addition to the known first-harmonic excitation.
In contrast to the experimentally observed second-harmonic response in harmonic Hall measurements of spin-orbit
torque in magnetic thin films, this second-harmonic response directly originates from spin-orbit torque driven
domain wall dynamics. Based on the spin current generated by domain wall dynamics, the longitudinal spin
motive force generated voltage across the length of the nanowire is determined. The second-harmonic response
introduces additionally a practical field-free and all-electrical method to probe the effective spin Hall angle for
FM/NM bilayer structures that could be applied in experiments. Our results also demonstrate the capability of
utilizing FM/NM bilayer structures in domain wall based spin-torque signal generators and resonators.
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