Spin-orbit-proximitized ferromagnetic metal by monolayer transition metal dichalcogenide: Atlas of spectral functions, spin textures, and spin-orbit torques in Co/MoSe₂, Co/WSe₂ and Co/TaSe₂ heterostructures

Journal Article · Mon Oct 19 00:00:00 EDT 2020 · Physical Review Materials

DOI:https://doi.org/10.1103/physrevmaterials.4.104007· OSTI ID:1852216

Dolui, Kapildeb  ^[1]; Nikolić, Branislav K.  ^[1]

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1. Univ. of Delaware, Newark, DE (United States)

In this work, the heterostructures composed of an ultrathin ferromagnetic metal (FM) and a material hosting strong spin-orbit (SO) coupling are the principal resource for SO torque and spin-to-charge conversion nonequilibrium effects in spintronics. The key quantity in theoretical description of these effects is nonequilibrium spin density, which can appear on any monolayer of the heterostructure through which the current is flowing as long as the monolayer bands are affected by the native or proximity induced SO coupling. Here we demonstrate how hybridization of wave functions of Co layer and a monolayer of transition metal dichalcogenides (TMDs)—such as semiconducting MoSe₂ and WSe₂ or metallic TaSe₂—can lead to dramatic transmutation of electronic and spin structure of Co within some distance away from its interface with TMD, when compared to the bulk of Co or its surface in contact with a vacuum. This is due to proximity induced SO splitting of Co bands encoded in the spectral functions and spin textures on its monolayers, which we obtain using noncollinear density functional theory (ncDFT) combined with equilibrium Green function (GF) calculations. In fact, SO splitting is present due to structural inversion asymmetry of the bilayer—i.e., just the presence of the interface—even if SO coupling within TMD monolayer is artificially switched off in ncDFT calculations. However, switching it on makes the effects associated with proximity SO coupling within Co layer about five times larger. Injecting spin-unpolarized charge current through SO-proximitized monolayers of Co generates nonequilibrium spin density over them, so that its cross product with the magnetization of Co determines SO torque. The SO torque computed via first-principles quantum transport methodology, which combines ncDFT with nonequilibrium GF calculations, can be used as the screening parameter to identify optimal combination of materials and their interfaces for applications in spintronics. In particular, we identify heterostructure two-monolayer-Co/monolayer-WSe₂ as the most optimal one, at least in the clean limit.

• Research Organization: Univ. of Delaware, Newark, DE (United States)
• Sponsoring Organization: USDOE Office of Science (SC); National Science Foundation (NSF)
• Grant/Contract Number: SC0016380; ACI-1053575
• OSTI ID: 1852216
• Alternate ID(s): OSTI ID: 1886898
• Journal Information: Physical Review Materials, Vol. 4, Issue 10; ISSN 2475-9953
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
materials science
spin transfer torque
spin-orbit coupling
spintronics
2-dimensional systems
magnetic multilayers
solid-solid interfaces
transition metal dichalcogenides
density functional theory
nonequilibrium Green's function
spin orbit proximity effect
transition metal dichalcogenide
spectral function
spin texture
spin orbit torque