Engineering Proximity Exchange by Twisting: Reversal of Ferromagnetic and Emergence of Antiferromagnetic Dirac Bands in Graphene/Cr2Ge2Te6

We investigate the twist-angle and gate dependence of the proximity exchange coupling in twisted graphene on monolayer Cr2Ge2Te6 from first principles. The proximitized Dirac band dispersions of graphene are fitted to a model Hamiltonian, yielding effective sublattice-resolved proximity-induced exchange parameters (AAex and ABex) for a series of twist angles between 0 degrees and 30 degrees. For aligned layers (0 degrees twist angle), the exchange coupling of graphene is the same on both sublattices, AAex ABex 4 meV, while the coupling is reversed at 30 degrees (with AAex ABex -4 meV). Remarkably, at 19.1 degrees the induced exchange coupling becomes antiferromagnetic: AAex 0, ABex 0. Further tuning is provided by a transverse electric field and the interlayer distance. The predicted proximity magnetization reversal and emergence of an antiferromagnetic Dirac dispersion make twisted graphene/Cr2Ge2Te6 bilayers a versatile platform for realizing topological phases and for spintronics applications.