I. Introduction
Magnetic domains are moved by the spin-transfer torque (STT) arising from a spin-polarized current (SPC) [1]–[5]. The phenomenon of magnetic domain motion is used in racetrack memory and domain wall (DW) motion-type magnetic memory, as well as others, which have attracted considerable attention as spintronic devices, particularly because of the very high potential storage densities they can offer [6]. It is assumed that magnetic domains can be used as binary digits in racetrack memory.