Control of skyrmion movement in nanotrack by using periodic strain

Abstract

Magnetic skyrmions are a topologically stable and particle-like chiral spin configuration. They are appealing because of their potential applications in racetrack memory and other spintronic devices. These applications are strongly dependent on the skyrmion motion in confined geometry. Therefore, it is important to study the moving behaviors of skyrmions in a nanotrack to make them have more practical applications. Mechanical strain and stress have been demonstrated theoretically and experimentally to be able to effectively control the skyrmion phase. It can stabilize the skyrmion lattice in a broad range, and change the shape of the skyrmion crystal. In this paper, we study the moving behaviors of ferromagnetic skyrmions and antiferromagnetic skyrmions under the action of sinusoidally distributed strain in a nanotrack by using micromagnetic simulation. We assume that strain is uniaxial and perpendicular to the plane of the nanotrack. Its strength varies sinusoidally along the x-axis. Meanwhile, we apply an in-pane current along the nanotrack to drive the skyrmion moving towards the right side. We first find that there is a threshold current density that is defined as the minimum current that can drive skyrmion moving continuously. When the current density is larger than the threshold current density, the skyrmion can move continuously in the nanotrack. The threshold current density increases with the amplitude of strain increasing, but decreases with the period of strain increasing. Second, we find that the trajectory of skyrmion changes under the action of the sinusoidal distributed strains. For ferromagnetic skyrmion, its trajectory changes from straight line to periodic wavy line. Also, we find that the longitudinal velocity of skyrmion is affected by the boundary of the nanotrack. When the skyrmion is close to the upper boundary of the nanotrack, the longitudinal velocity increases sharply and it will form a peak in the velocity curve, but when the skyrmion is close to the lower boundary of the nanotrack, the longitudinal velocity decreases and it will form a valley in the velocity curve. The transverse velocity of skyrmion relates to the strain gradient. It is inversely proportional to the strain gradient. For antiferromagnetic skyrmion, we find that the movement trajectory of antiferromagnetic skyrmion does not change under the stress control. However, its diameter and velocity change periodically. Its velocity can vary between 103 m/s and 0. Our results demonstrate that the sinusoidal strain can control the skyrmion motion. This work may provide guidance in designing and developing of the spintronic devices based on magnetic skyrmions.