Theory of Stabilization and Adiabatic Current Drive of Skyrmions in Synthetic Antiferromagnets
ORAL
Abstract
Skyrmions in synthetic antiferromagnetically (SAF) coupled multilayers have shown great promise for next-generation applications that require fast response and energy-efficient operation. Their dynamic stability against topological Hall effect and their immunity to stray fields make them candidates for applications in memory and logic devices. The conditions needed for stabilizing SAF skyrmions and how this stability depends on the material parameters and external drive conditions are not well understood.
Here, we provide the theory of stabilizing SAF skyrmions by extending the ferromagnetic skyrmion theory to antiferromagnetically coupled FM/NM/FM multilayers (here: Co/CoFeB/Ir/CoFeB/Co). Our micromagnetic model results indicate that the material parameters such as saturation magnetization, Dzyaloshinskii–Moriya interaction constant, uniaxial anisotropy, and interlayer exchange can yield equilibrium skyrmion radii between 1-50 nm. Skyrmions on both ferromagnetic layers are stabilized based on the balance of interlayer and intralayer exchange, shape, uniaxial (Ku), Zeeman, and Dzyaloshinskii–Moriya interaction anisotropy energy. The skyrmion stability strongly depends on Ms, Ku, and DMI constants.
Next, we investigated the effect of perpendicular external current drive and the out-of-plane external magnetic field on the skyrmion velocity, SAF skyrmion decoupling thresholds, and the adiabatic drive. Increasing external magnetic field (until 120 mT) triggers SAF skyrmion velocities as high as 196 m s-1. The skyrmions on both sides decouple when the current density is 4x1011 A m-2 and this decoupling current decreases with the external magnetic field. The phase diagram of skyrmion velocity under different magnetic field and current bias indicates that the skyrmions can be driven with currents between 108–3x1011 A m-2 without topological Hall effect or decoupling.
These results could pave the way for new understanding of functional SAF skyrmions and their applications.
Here, we provide the theory of stabilizing SAF skyrmions by extending the ferromagnetic skyrmion theory to antiferromagnetically coupled FM/NM/FM multilayers (here: Co/CoFeB/Ir/CoFeB/Co). Our micromagnetic model results indicate that the material parameters such as saturation magnetization, Dzyaloshinskii–Moriya interaction constant, uniaxial anisotropy, and interlayer exchange can yield equilibrium skyrmion radii between 1-50 nm. Skyrmions on both ferromagnetic layers are stabilized based on the balance of interlayer and intralayer exchange, shape, uniaxial (Ku), Zeeman, and Dzyaloshinskii–Moriya interaction anisotropy energy. The skyrmion stability strongly depends on Ms, Ku, and DMI constants.
Next, we investigated the effect of perpendicular external current drive and the out-of-plane external magnetic field on the skyrmion velocity, SAF skyrmion decoupling thresholds, and the adiabatic drive. Increasing external magnetic field (until 120 mT) triggers SAF skyrmion velocities as high as 196 m s-1. The skyrmions on both sides decouple when the current density is 4x1011 A m-2 and this decoupling current decreases with the external magnetic field. The phase diagram of skyrmion velocity under different magnetic field and current bias indicates that the skyrmions can be driven with currents between 108–3x1011 A m-2 without topological Hall effect or decoupling.
These results could pave the way for new understanding of functional SAF skyrmions and their applications.
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Publication: Rawana Yagan, Mehmet C. Onbasli, "Theory of stabilization and adiabatic current drive of skyrmions in SAF" (Submitted)
Presenters
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Rawana Yagan
Koc University
Authors
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Rawana Yagan
Koc University
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Mehmet Cengiz Onbasli
Koc University