Skyrmion Hall effect and shape deformation of current-driven bilayer skyrmions in synthetic antiferromagnets

TL;DR

This paper investigates the skyrmion Hall effect and shape deformation in bilayer skyrmions within synthetic antiferromagnets, revealing that certain skyrmion types exhibit a finite Hall angle under specific conditions, with implications for memory devices.

Contribution

The study introduces a Lagrangian formalism to explain the skyrmion Hall effect in bilayer skyrmions and demonstrates the deformation and Hall angle dependence on skyrmion type and torque.

Findings

Bloch-type bilayer skyrmions have a finite Hall angle under spin-orbit torque.

Néel-type skyrmions do not exhibit a Hall angle in this context.

Current induces elliptical deformation aligned with skyrmion velocity.

Abstract

The commonly believed absence of skyrmion Hall effect for topologically trivial magnetic skyrmions is reconsidered for bilayer skyrmions in synthetic antiferromagnets driven by spin-transfer and spin-orbit torques. Using a general Lagrangian formalism, we show that Bloch-type bilayer skyrmions acquire a finite Hall angle when driven by spin-orbit torque, while N\'{e}el-type skyrmions do not, in agreement with micromagnetic simulations. Both types of skyrmions exhibit current-induced elliptical deformation with minor and major axes aligned longitudinally and transversely to their velocity, respectively. A linear relation between velocity and longitudinal radius is derived with a coefficient proportional to the strength of spin-orbit torque. These effects are critical for antiferromagnetic skyrmion-based applications such as skyrmion racetrack memory. The Lagrange equations also reproduce the linear Hall angle-helicity relation reported by Msiska et al., Phys. Rev. Appl. 17, 064015 (2022). An intuitive explanation of the skyrmion Hall effect for arbitrary helicity based on the antiferromagnetic exchange torque is also provided.