Abstract
In recent years, there has been a growing interest in spin-orbit torques (SOTs) for manipulating the magnetization in nonvolatile magnetic memory devices. SOTs rely on the spin-orbit coupling of a nonmagnetic material coupled to a ferromagnetic layer to convert an applied charge current into a torque on the magnetization of the ferromagnet (FM). Transition metal dichalcogenides (TMDs) are promising candidates for generating these torques with both high charge-to-spin conversion ratios, and symmetries and directions which are efficient for magnetization manipulation. Moreover, TMDs offer a wide range of attractive properties, such as large spin-orbit coupling, high crystalline quality and diverse crystalline symmetries. Although numerous studies were published on SOTs using TMD/FM heterostructures, we lack clear understanding of the observed SOT symmetries, directions, and strengths. In order to shine some light on the differences and similarities among the works in literature, in this mini-review we compare the results for various TMD/FM devices, highlighting the experimental techniques used to fabricate the devices and to quantify the SOTs, discussing their potential effect on the interface quality and resulting SOTs. This enables us to both identify the impact of particular fabrication steps on the observed SOT symmetries and directions, and give suggestions for their underlying microscopic mechanisms. Furthermore, we highlight recent progress of the theoretical work on SOTs using TMD heterostructures and propose future research directions.
Highlights
Spin-orbit torques (SOTs) are promising candidates for effective manipulation of magnetization through electric currents with applications in nonvolatile magnetic memory and logic devices
The observed torques in Transition metal dichalcogenides (TMDs)/FM heterostructures cannot always be explained by well-known effects such as the bulk spin Hall effect (SHE) (Dyakonov and Perel, 1971; Hirsch, 1999; Sinova et al, 2015) or the interfacial Rashba-Edelstein Effect (REE) (Edelstein, 1990; Ganichev et al, 2002; Kato et al, 2004; Mihai Miron et al, 2010; Ganichev et al, 2016) (Figure 1), indicating that other mechanisms involving material specific properties or interfacial effects are into play
We have given an overview of the current status of the field of SOTs in TMD/FM heterostructures
Summary
Spin-orbit torques (SOTs) are promising candidates for effective manipulation of magnetization through electric currents with applications in nonvolatile magnetic memory and logic devices. The observed torques in TMD/FM heterostructures cannot always be explained by well-known effects such as the bulk spin Hall effect (SHE) (Dyakonov and Perel, 1971; Hirsch, 1999; Sinova et al, 2015) or the interfacial Rashba-Edelstein Effect (REE) (Edelstein, 1990; Ganichev et al, 2002; Kato et al, 2004; Mihai Miron et al, 2010; Ganichev et al, 2016) (Figure 1), indicating that other mechanisms involving material specific properties or interfacial effects are into play This is supported by recent works suggesting that both the type of ferromagnetic layer (Dolui and Nikolic, 2020; Go and Lee, 2020) and the interface properties between the TMD and the ferromagnetic layer (Amin et al, 2020; Sousa et al, 2020; Go et al, 2020) (Sahoo et al, 2020; Kumar et al, 2020; Xue et al 2020) are of paramount importance for the observed SOTs, allowing for enhanced and unconventional SOTs. To describe to different torques, we use the notation in terms of odd (τζo ∝ m × ζ ) or even (τζe ∝ m × ( ζ × m)) with respect to the magnetization direction (m), with ζ x, y, z. ), because the electric field across the device can be more accurately determined when compared to the current density (Nguyen et al, 2016)
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