Quaternary memory based on magnetic skyrmion

Abstract

Magnetic skyrmions are nanoscale spin textures that are highly stable due to their protected topo-logical charge [1-2]. Skyrmions also experience almost no intrinsic pinning, allowing them to be easily manipulated with low current densities. These positive attributes allows the skyrmion to a very attractive candidate for next generation memory devices [2-4]. In this work, we demonsrate by micromagnetic simulations [5] that a skyrmion can be excited to move in a gyrotropic fashion with the application of a spin-polarized current perpendicular to the nanodisk. In a patterned nanodisk (see Fig. 1), the gyrotropic motion can be exploited to create a four-state memory device. Due to repulsive edge interactions, the skyrmion is forced to reside in one of the 4 quadrants of the device. The four possible positions of the skyrmion represents the four states of our device. To alter the state, a perpendicular current can be applied to drive the skyrmion into either of its neighboring quadrant, depending on the current density and pulse duration. Fig. 2 shows the relative position of the skyrmion against the pulse duration of the applied current density (the material parameters are chosen similar to Ref. 4). Starting from position 0 marked in Fig. 1, we showed that it is possible to move the skyrmion into different quadrants by varying the pulse duration. A marginal increase in applied current density was able to produce a significant decrease in pulse duration required for shifting the device's state. Figure 1(b) shows the trajectory of skyrmion core with current density J = 4E10 A/m2 and pulse duration t = 4.5 ns, which reveal that skyrmion moves away from position 0 and finally relaxes at position 2. Our proposed device has the advantage of having a low threshold current-density for state-switching and very small size (as small as about 50 nm). The solution provided in this work will facilitate the creation of high density skyrmion-based devices.