Abstract
Spin‐orbit torque (SOT) opens an efficient and versatile avenue for the electrical manipulation of magnetization in spintronic devices. The enhancement of SOT efficiency and reduction of power consumption are key points for the implementation of high‐performance SOT devices, which strongly rely on the spin‐orbit coupling (SOC) strength and magnetic properties of ferromagnetic/non‐magnetic heterostructures. Recently, van der Waals‐layered materials have shown appealing properties for use in efficient SOT applications. On the one hand, transition‐metal dichalcogenides, topological insulators, and graphene‐based heterostructures possess appreciable SOC strength. This feature can efficiently converse the charge current into spin current and result in large SOT. On the other hand, the newly discovered layered magnetic materials provide ultra‐thin and gate‐tunable ferromagnetic candidates for high‐performance SOT devices. In this review, the latest advancements of SOT research in various layered materials are summarized. First, a brief introduction of SOT is given. Second, SOT studies of various layered materials and heterostructures are summarized. Subsequently, progresses on SOT‐induced magnetization switching are presented. Finally, current challenges and prospects for future development are suggested.
Highlights
The discoveries of giant magnetoresistance and tunnel magne- ical SOT structure comprises a ferromagnetic (FM) layer and a toresistance (TMR) have significantly improved the storage den- normal metal (NM) layer
NbSe2 is a fully metallic transition metal dichalcogenides (TMDs) with strong spin-orbit coupling (SOC) and σe ≈ 6 × 105 (Ωm)−1.[81]. Using the spin-torque-ferromagnetic resonance (ST-FMR) approach, conventional SOT was observed in a NbSe2/Py heterostructure (Figure 5a), and the corresponding spin conductivity was estimated as ≈4 × 104 (ħ/2e)(Ωm)−1.[82]. Interestingly, based on the symmetry requirements, unconventional SOT was prohibited in the heterostructure because of its highly symmetric structure
Current-induced SOT offers a powerful tool for efficiently controlling magnetization without external magnetic fields, and it allows the realization of high-performance spintronic devices, such as SOT-MRAM
Summary
(SOT), has recently emerged as a promising technique for efficient magnetization manipulation.[10,11,12] A typ-. Another promising candidate is the family of topological insulators (TIs) Owing to their topologically non-trivial surface states, TIs possess extremely large SOT efficiencies, which are several orders of magnitude larger than those of conventional HMs.[30,31] This large SOT efficiency allows for low-power magnetization manipulation.[32] In addition to TMDs and TIs, graphene-based hybrid heterostructures have recently been proposed as suitable spin sources for SOT applications.[33,34,35] Pristine graphene has been extensively studied as a spin transport channel owing to its long spin diffuse length and high electron mobility.[36] Despite its considerably weak SOC, several studies have revealed that the enhancement of SOC in graphene is feasible via the extrinsic effect.[37,38] the combination of graphene with other materials having strong SOC can give rise to graphenebased heterostructures with strong SOC.[38,39,40] Such enhanced SOC result in appreciable charge-spin interconversions, and they can be further tuned by an electric field.[35,41,42] Most importantly, in graphene-based heterostructures, high electron mobility can be maintained while enhancing the SOC. We discuss current challenges and future perspectives for this emerging field
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