Band-structure spin-filtering in vertical spin-valves based on chemical vapor deposited WS_2
Spin transport in WS2-based 2D-magnetic tunnel junctions (2D-MJTs) is reported, unveiling a band structure spin filtering effect specific to the transition metal dichalcogenides (TMDCs) family. WS2 mono-, bi-, and tri-layers are derived by a chemical vapor deposition process, and then integrated in complete Co/Al2O3/WS2/Co MTJ hybrid spin-valve structures. A tunnel Co/Al2O3 spin analyser is used to probe the extracted spin-polarised current from the WS2/Co interface and its evolution as a function of WS2 layer thicknesses. For monolayer WS2, the largest spin signal is reported for a TMDC-based spin valve, corresponding to a spin polarisation of PCo/WS2 = 12%. Interestingly, for bi- and tri-layer WS2, the spin signal is reversed, which indicates a switch in the mechanism of interfacial spin extraction.
With the support of ab initio calculations, Dr. Simon Dubois in the group of J.-C. Charlier proposed a model to address the experimentally measured inversion of the spin polarization based on the change in the WS2 band structure while going from monolayer (direct bandgap) to bilayer (indirect bandgap). These experimental and theoretical results illustrate the rich potential of the families of semiconducting 2D materials for the control of spin currents in 2D-MTJs.
Référence : V. Zatko, et al., ACS Nano 13, 14468-14476 (2019)