Nucleation and manipulation of single skyrmions using spin-polarized currents in antiferromagnetic skyrmion-based racetrack memories

Abstract

In this work, an ultrafast nucleation of an isolated anti-ferromagnetic (AFM) skyrmion was reported in an AFM layer with DMi strengths of 0.47$$-$$ - 0.32 $$\mathrm{mJ}/{\mathrm{m}}^{2}$$ mJ / m 2 using spin-transfer torque by locally injecting pure spin currents into magnetic tracks. Besides, we revealed the key advantages of AFM skyrmion-based racetrack memories by comparing the motion of AFM and FM skyrmions driven by spin–orbit torques (SOTs) for different skyrmion sizes along racetrack memories with various notch sizes. Our results indicate that for AFM skyrmion, the skyrmion Hall effect does not exist during the skyrmion motion, therefore at small skyrmion sizes, we succeeded to overcome the repulsive forces developed in the notch area for low and large SOTs. The obtained findings were carefully analyzed by computing the variation of energy barriers associated with the notch for different skyrmion sizes using minimum energy path (MEP) calculations. We showed that the larger the skyrmion size, the harder it is to shrink the skyrmion in the notch which produces a high energy barrier (Eb) for large skyrmion sizes. Moreover, as the notch size increases, the skyrmion size shrinks further, and hence Eb increases proportionally. Nevertheless, we proved that AFM skyrmions are more efficient and flexible than FM skyrmions against boundary forces.

Reconfigurable Skyrmion-Based Logic Gates: Versatile Design and Full-Scale Implementation

“…Notably, the coupled skyrmions enable intriguing interactions and functionalities. However, they possess a unique skyrmion number, which is represented by its topological number equal to zero (Figure e). , Nevertheless, when considering the individual sublattices A and B, the topological number of the AFM skyrmion, denoted as Q AFM (eq ), can be determined using a discretized version that accounts for the opposite core polarities . This discretized version provides insight into the behavior of the skyrmion, highlighting its remarkable features, such as inherent topological protection and the influence of the AFM exchange interaction Q AFM τ = prefix− 1 4 π ∑ ijk m i τ · ( bold-italicm bold-italicj bold-italicτ × bold-italicm bold-italick bold-italicτ ) , τ = A , B …”

“…To ensure accurate and efficient analysis, we discretize the simulated models into tetragonal elements measuring 1 × 1 × 1 nm 3 , utilizing the finite difference method. This discretization technique allows us to precisely capture the intricate nanoscale behavior . By making the grid size small enough, we can numerically mimic the atomistic model conditions to effectively simulate antiferromagnetic systems , (see Supporting Movie S1).…”

“…Antiferromagnetic (AFM) skyrmions have garnered significant attention due to their unique properties, rendering them highly desirable for various applications. These properties encompass fast nucleation and ultralow-power consumption, , enabling swift encoding and positioning AFM skyrmions as energy-efficient contenders for next-generation memory devices. Moreover, their high thermal stability allows for reliable operation at room temperature (RT). , Several investigations have unveiled the presence of skyrmions within AFM systems at RT and also advanced a variety of methods for precise control, such as current injection and ultrafast laser excitation, for both nucleation and manipulation. , In the quest to host and stabilize AFM skyrmions, various AFM materials have been explored including Mn 2 Au, CuMnAs, IrMn 3 , and MnBi 2 Te 4 . − Indeed, AFM materials are markedly limited in comparison to their FM counterparts, mainly due to the significant challenges inherent in their precise magnetic order, complex crystal structures, and thermal stability.…”

“…To address these challenges, multiple strategies have been explored. − One promising avenue involves the application of sputtering deposition techniques to fabricate highly oriented, textured D0 19 -type Mn 3 Sn films with a smooth surface by depositing polycrystalline Mn–Sn onto metallic seed layers, such as Pt or Cu . Remarkably, these efforts have contributed to revealing a distinctive characteristic of skyrmions in AFM materials, notably the absence of the skyrmion Hall effect (SkHE) owing to the compensated skyrmion topological charge. ,, Consequently, AFM skyrmions maintain their longitudinal trajectory in the AFM track memory, unaffected by deflection perpendicular to the current flow. This unique characteristic positions them as potentially good candidates for advanced technologies in magnetic data storage and processing, including AFM skyrmion-based memories, AFM skyrmion logic gates, and AFM skyrmion diodes. − Additionally, AFM skyrmions hold considerable promise in bioinspired computing, particularly in their application to the development of neuromorphic computing devices. , …”

Magnetic skyrmions and domain walls for logical and neuromorphic computing

“…Magnetic skyrmions as topological information carriers have been widely explored for integration in emerging computing systems. Specifically, [22,30,[49][50][51][52] use skyrmions for memory, [53][54][55][56][57][58][59][60] use skyrmions for logic gates, and [61][62][63][64][65] use skyrmions for neuromorphic computing applications. This section focuses on skyrmion logic gates and the associated driving scheme, while the following section shifts the focus to skyrmions in neuromorphic computing systems.…”