Abstract
Transition metal dichalcogenides (TMDs) are promising materials for efficient generation of current-induced spin-orbit torques (SOTs) on an adjacent ferromagnetic layer. Numerous effects, both interfacial and bulk, have been put forward to explain the different torques previously observed. Thus far, however, there is no clear consensus on the microscopic origin underlying the SOTs observed in these TMD/ferromagnet bilayers. To shine light on the microscopic mechanisms at play, here we perform thickness dependent SOT measurements on the semiconducting WSe2/permalloy bilayer with various WSe2 layer thickness, down to the monolayer limit. We observe a large out-of-plane field-like torque with spin-torque conductivities up to . For some devices, we also observe a smaller in-plane antidamping-like torque, with spin-torque conductivities up to , comparable to other TMD-based systems. Both torques show no clear dependence on the WSe2 thickness, as expected for a Rashba system. Unexpectedly, we observe a strong in-plane magnetic anisotropy—up to about erg cm−3—induced in permalloy by the underlying hexagonal WSe2 crystal. Using scanning transmission electron microscopy, we confirm that the easy axis of the magnetic anisotropy is aligned to the armchair direction of the WSe2. Our results indicate a strong interplay between the ferromagnet and TMD, and unveil the nature of the SOTs in TMD-based devices. These findings open new avenues for possible methods for optimizing the torques and the interaction with interfaced magnets, important for future non-volatile magnetic devices for data processing and storage.
Highlights
The electrical manipulation of magnetic layers is extremelly appealing for future non-volatile and energyefficient data processing and memory devices [1] [2] [3]
The values we find for HHAA for these devices are higher by factors of 2 to 10 than for those reported in similar systems [19] [20] [22] [23]
The appearance of a weaker damping-like torque in these systems confirms the prediction of recent theoretical work on similar interfacial Rashba systems including scattering, and accentuates the importance of the heavy metal/ferromagnet interface quality for tayloring towards highly efficient torques
Summary
The electrical manipulation of magnetic layers is extremelly appealing for future non-volatile and energyefficient data processing and memory devices [1] [2] [3]. One of the key components of materials showing large SOTs is the presence of a high spin-orbit coupling. For this reason, heavy-metal layers such as Pt [4] [5], W [6] [7], and Ta [8], have been used to generate efficient SOTs. For this reason, heavy-metal layers such as Pt [4] [5], W [6] [7], and Ta [8], have been used to generate efficient SOTs These systems were shown to be capable of switching the direction of out-of-plane magnetic layers with relatively small current densities Heavy-metal-based SOT devices have been in the spotlight for future magnetic random-access memory devices [2]
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