Design of a novel bilayered structure of ferromagnetic metal and nonmagnetic insulator wires while maintaining the distance between the constituent skyrmions

Abstract

Magnetic-skyrmion-based racetrack memory is a high-density memory for storing information driven by low-power, wherein the arrangement of skyrmions is stored in the form of binary digit combinations. This arrangement is altered based on the skyrmion motion resulting from the influence of the spin-transfer torque. We propose a novel layered structure of a ferromagnetic metal (FM) wire/nonmagnetic insulator wire/FM wire in which the skyrmions move while maintaining the arrangement. It consists of two FM wires that are perpendicularly magnetized. One of these comprises several skyrmions, which act as binary digits (data skyrmions). The other wire constitutes a sufficient number of skyrmions that are closely packed and allow the spin-polarized current to flow. A dipole–dipole interaction acts between these two FM wires. The motion of the data skyrmion is induced by the current-induced motion of the packed skyrmion. The motion of skyrmions is simulated via micromagnetic approaches. The data skyrmions move while maintaining the distance between each skyrmion. The analog position of the data skyrmion is controlled by the current flowing through another wire. The stable data skyrmion motion has a threshold current. When the current is larger than the threshold current, the skyrmion breaks, and/or the distance between skyrmions breaks. The threshold current density is found to decrease with an increasing vacuum layer thickness and increase with increasing thickness of the FM wire flowing current. Our results show that the skyrmion motion in the proposed structure can drive skyrmions with a spin-current density lower than that of the coupled granular/continuous structure and the edge-notched nanowire structure. This structure can be used in developing low-power operational devices based on skyrmion motion.