Spin relaxation and proximity effect in WS₂/graphene/fluorographene non-local spin valves

Control of the spin relaxation in graphene-based structures is necessary to achieve the envisioned utility of graphene in future spintronic devices beyond Moore’s law. Proximity induced spin relaxation caused by contact to a high spin-orbit material, such as WS₂, offers a promising avenue to manipulate the spin lifetime [1]. We demonstrate the operation of WS₂/graphene/fluorographene non-local spin valves and extract the spin lifetimes for a range of carrier concentrations by Hanle effect measurements. Four-terminal charge transport measurements allow us to calculate the momentum relaxation time as a function of carrier concentration and compare it to the spin lifetime. These data show that the D’yakonov-Perel’ mechanism is the dominant spin relaxation mechanism for WS₂/graphene/fluorographene devices. Without WS₂, linear scaling between the spin and momentum lifetimes points to spin-flip scattering during strong elastic scattering events strongly coupled to the electron spin. We attribute the change in spin relaxation type in part with the inclusion of WS₂ as a substrate to proximity induced spin-orbit coupling due to the adjacent WS₂ layer, and we compare our data to the literature. [1] A.L. Friedman, et al. Carbon 131, 18-25 (2018).