  Graphene sandwiched between semiconducting monolayers of ferromagnet
Cr$_2$Ge$_2$Te$_6$ and transition-metal dichalcogenide WS$_2$ acquires both
spin-orbit (SO), of valley-Zeeman and Rashba types, and exchange couplings.
Using first-principles combined with quantum transport calculations, we predict
that such doubly proximitized graphene within van der Waals heterostructure
will exhibit SO torque driven by unpolarized charge current. This system
lacking spin Hall current, putatively considered to be necessary for efficient
damping-like (DL) SO torque that plays a key role in magnetization switching,
demonstrates how DL torque component can be generated solely by skew-scattering
off spin-independent potential barrier or impurities in purely two-dimensional
electronic transport due to the presence of proximity SO coupling and its spin
texture tilted out-of-plane. This leads to current-driven nonequilibrium spin
density emerging in all spatial directions, whose cross product with proximity
magnetization yields DL SO torque, unlike the ballistic regime with no
scatterers in which only field-like (FL) SO torque appears. In contrast to SO
torque on conventional metallic ferromagnets in contact with three dimensional
SO-coupled materials, the ratio of FL and DL torque can be tuned by more than
an order of magnitude via combined top and back gates.
