Large Damping-Like Spin–Orbit Torque in a 2D Conductive 1T-TaS₂ Monolayer

Abstract

A damping-like spin-orbit torque (SOT) is a prerequisite for ultralow-power spin logic devices. Here, we report on the damping-like SOT in just one monolayer of the conducting transition-metal dichalcogenide (TMD) TaS 2 interfaced with a NiFe (Py) ferromagnetic layer. The charge-spin conversion efficiency is found to be 0.25 ± 0.03 in TaS 2 (0.88)/Py(7), and the spin Hall conductivity is found to be superior to values reported for other TMDs. We also observed sizable field-like torque in this heterostructure. The origin of this large damping-like SOT can be found in the interfacial properties of the TaS 2 /Py heterostructure, and the experimental findings are complemented by the results from density functional theory calculations. It is envisioned that the interplay between interfacial spin–orbit coupling and crystal symmetry yielding large damping-like SOT. The dominance of damping-like torque demonstrated in our study provides a promising path for designing the next-generation conducting TMD-based low-powered quantum memory devices.

Two-Dimensional Van Der Waals Materials for Spin-Orbit Torque Applications

“…The preparation of 2D materials by magnetron sputtering is usually performed in multiple steps while controlling strict growth and annealing conditions. To date, 2D materials for SOT devices prepared by sputtering include PtTe 2 (Xu et al, 2020) and TaS 2 (Husain et al, 2020a). Waferscale PtTe 2 films are prepared through a two-step process, which has been previously used for fabricating PtSe 2 (Wang et al, 2015;Yim et al, 2016) and WTe 2 (Zhou et al, 2017).…”

“…They are then transformed into uniform and homogenous PtTe 2 thin films by annealing them in tellurium vapour. Similarly, for TaS 2 (Husain et al, 2020a), as-deposited Ta ultra-thin films are transferred to a high vacuum chamber for the plasma-assisted sulfurization process. It is noted that the spin Hall conductivity of PtTe 2 and TaS 2 prepared by sputtering are superior to values reported for many other 2D vdW materials, denoting the high-quality of 2D vdW materials prepared by the sputtering method.…”

“…Besides, an in-plane field-like torque is observed and varies from sample to sample, consisting of the symmetry breaking by a uniaxial strain that might result from device fabrication. Another metallic 2D vdW material used for SOT applications is TaS 2 (Husain et al, 2020a), which exhibits to date the lowest room-temperature resistivity (≈16.9 μΩ cm) among metallic TMDs (Figure 2E). The SOTs were measured by using both ST-FMR and SHH, and the damping-like SOT (Lv et al, 2018).…”

“…(D) Antisymmetric components of the ST-FMR spectra detected at a magnetic field with different directions when the electric current is applied parallel to the low-symmetry crystal axis. (E) DC-induced changes of effective damping in the TaS 2 /Py heterostructure for positive and negative field directions (Husain et al, 2020a). (F) Harmonic Hall voltage detected at a magnetic field of 34 mT with different angles.…”

Separation of Artifacts from Spin‐Torque Ferromagnetic Resonance Measurements of Spin‐Orbit Torque for the Low‐Symmetry Van der Waals Semi‐Metal ZrTe3

“…More recently, spin-orbit torques generated by van der Waals materials have been an increasing focus, in order to study the consequences of spin-momentum coupling in topological materials and to generate spin-orbit torques with unconventional orientation using low-symmetry materials. Recent experiments in these categories include studies of transition metal dichalcogenides MoS 2 , [18][19][20] WTe 2 , [21][22][23][24] WS 2 , [25] NbSe 2 , [26] TaTe 2 , [27] MoTe 2 , [28][29][30] DOI: 10.1002/qute.202100111 PtTe 2 , [31] TaSe 2 , [32] WSe 2 , [33,34] and Cd 3 As 2 , [35] as well as studies of the topological insulators Bi 2 Se 3 , [36][37][38] BiSb, [39] and magnetically-doped BiSbTe. [40,41] When devices are made from exfoliated samples of van der Waals materials, it can sometimes be difficult to isolate layers thinner than a few 10's of nanometers, so the spin-orbit layers can be much thicker than for typical measurements of heavy metals, where the spin-orbit layers are generally much thinner than 10 nm.…”