Multi-segmented nanowires for vortex magnetic domain wall racetrack memory

Abstract

A vortex domain wall’s (VW) magnetic racetrack memory’s high performance depends on VW structural stability, high speed, low power consumption and high storage density. In this study, these critical parameters were investigated in magnetic multi-segmented nanowires using micromagnetic simulation. Thus, an offset magnetic nanowire with a junction at the center was proposed for this purpose. This junction was implemented by shifting one portion of the magnetic nanowire horizontally in the x-direction (l) and vertically (d) in the y-direction. The VW structure became stable by manipulating magnetic properties, such as magnetic saturation (M s) and magnetic anisotropy energy (K u). In this case, increasing the values of M s ≥ 800 kA/m keeps the VW structure stable during its dynamics and pinning and depinning in offset nanowires, which contributes to maintenance of the storage memory’s lifetime for a longer period. It was also found that the VW moved with a speed of 500 m/s, which is desirable for VW racetrack memory devices. Moreover, it was revealed that the VW velocity could be controlled by adjusting the offset area dimensions (l and d), which helps to drive the VW by using low current densities and reducing the thermal-magnetic spin fluctuations. Further, the depinning current density of the VW (J d) over the offset area increases as d increases and l decreases. In addition, magnetic properties, such as the M s and K u, can affect the depinning process of the VW through the offset area. For high storage density, magnetic nanowires (multi-segmented) with four junctions were designed. In total, six states were found with high VW stability, which means three bits per cell. Herein, we observed that the depinning current density (J d) for moving the VW from one state to another was highly influenced by the offset area geometry (l and d) and the material’s magnetic properties, such as the M s and K u.