Observation of asymmetry in domain wall velocity under transverse magnetic field

K.-J Kim,Y Yoshimura,T Okuno,Y Nakatani,T Ono,T Moriyama,K.-J Lee,S.-W Lee

doi:10.1063/1.4944897

K.-J Kim, Y Yoshimura + Show 6 more

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https://doi.org/10.1063/1.4944897

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Abstract

The dynamics of a magnetic domain wall (DW) under a transverse magnetic field Hy are investigated in two-dimensional (2D) Co/Ni microstrips, where an interfacial Dzyaloshinskii-Moriya interaction (DMI) exists with DMI vector D lying in +y direction. The DW velocity exhibits asymmetric behavior for ±Hy; that is, the DW velocity becomes faster when Hy is applied antiparallel to D. The key experimental results are reproduced in a 2D micromagnetic simulation, which reveals that the interfacial DMI suppresses the periodic change of the average DW angle φ even above the Walker breakdown and that Hy changes φ, resulting in a velocity asymmetry. This suggests that the 2D DW motion, despite its microscopic complexity, simply depends on the average angle of the DW and thus can be described using a one-dimensional soliton model. These findings provide insight into the magnetic DW dynamics in 2D systems, which are important for emerging spin-orbitronic applications.

Highlights

The dynamics of a magnetic domain wall (DW) under a transverse magnetic field Hy are investigated in two-dimensional (2D) Co/Ni microstrips, where an interfacial Dzyaloshinskii-Moriya interaction (DMI) exists with DMI vector D lying in + y direction
We show that the interfacial DMI generates an asymmetry in the DW velocity when the DW is driven by a perpendicular magnetic field under bias transverse magnetic fields
To identify the origin of the asymmetric behavior, we performed a micromagnetic simulation, which indicated that the interfacial DMI fixes the azimuthal angle of the dynamic DW even beyond the Walker breakdown (WB) and that the transverse magnetic field changes the azimuthal angle of the DW

Summary

Introduction

The dynamics of a magnetic domain wall (DW) under a transverse magnetic field Hy are investigated in two-dimensional (2D) Co/Ni microstrips, where an interfacial Dzyaloshinskii-Moriya interaction (DMI) exists with DMI vector D lying in + y direction. 2(a) and 2(b)) shows that the minimum DW velocity was observed at |Hx| = 290 ± 10 and 13 ± 1 mT for the asymmetric and symmetric Co/Ni microstrips, respectively, which correspond to the DMI-induced effective field Hdmi of each sample.[20] The value of D was calculated using the relation D = MSHdmi∆,8,18 where MS is the saturation magnetization and ∆ = A/ KU − 1/2μ0MS2 is the DW width parameter, with an exchange stiffness of A

Results

Conclusion