Spin-orbit-torque magnetic manipulation with 2D materials

Current-induced spin-orbit torques provide a promising strategy for efficient manipulation of nonvolatile magnetic memory and logic technologies. For best performance, both the layer of material that provides the spin-orbit torque and the magnetic layer being manipulated should be as thin as possible. Here we discuss experiments which probe the ultimate limits in which 2D materials are used for either the spin-orbit layer or the magnetic layer.

First, we discuss experiments in which the source of the spin-orbit torques are transition-metal dichalcogenide (TMD) materials with strong spin-orbit interactions, e.g., WTe₂, TaTe₂, MoTe₂, and NbSe₂. We demonstrate that the low crystalline symmetries of TMDs can allow components of spin-orbit torque that are forbidden for the more commonly-studied heavy metals and topological insulators. In particular, they can produce an out-of-plane antidamping torque of the type desired to drive the most efficient switching mode for magnets with perpendicular anisotropy. TMD materials with similar crystal structures can generate current-induced torques with a surprising range of contrasting symmetries, indicating that the torques depend not only on global broken symmetries but also on microscopic factors.

We will also discuss initial experiments in which recently-discovered 2D magnetic materials are integrated with spin-orbit materials. Using mechanically exfoliated thin flakes of the insulating 2D ferromagnet Cr₂Ge₂Te₆combined into a bilayer structure with tantalum, we have observed current-induced deflections of the out-of-plane magnetic moment of Cr₂Ge₂Te₆and characterized the strength of the spin-orbit torque.