Oblique drive tolerance of elliptical skyrmions moving in perpendicularly magnetized nanowire

Abstract

A magnetic skyrmion is stabilized via the Dzyaloshinskii–Moriya interaction in a perpendicularly magnetized thin nanowire. When the skyrmion is driven by a spin-transfer torque due to spin currents flowing through the wire, the skyrmion approaches the wire edge owing to the skyrmion Hall effect. In other words, the skyrmion moves obliquely along the longitudinal direction of the wire. The skyrmion often breaks or disappears because of this oblique motion. In this study, we propose an elliptical skyrmion to prevent this disappearance. We simulated the current-induced motion of an elliptical skyrmion produced in a wire through a micromagnetic approach. The elliptical skyrmion was also moved obliquely to the longitudinal direction of the wire. When a small current flowed through the wire, the skyrmion moved in the longitudinal direction of the wire after it approached the wire edge. When a larger current flowed through the wire, the skyrmion disappeared after it approached the wire edge. The elliptical skyrmion can be driven over a long distance with a larger current compared to a circular skyrmion. The motion of the skyrmion approaching the wire edge was analyzed using Thiele’s equation, with an external force. We estimated the external force from the simulation results of the skyrmion motion. The external force was proportional to the distance between the skyrmion edge and the wire edge. The results of this study indicate that using the elliptical skyrmion as a binary digit in a magnetic memory, such as a skyrmion-based racetrack memory, can be advantageous in term of the stability of the binary digit.