Rashba-type Dzyaloshinskii-Moriya interaction in h-BN/Co and graphene/Co heterostructures

With the recently observed chiral domain wall structures at the graphene/ferromagnet interfaces [1,2], the Dzyaloshinskii-Moriya interaction (DMI) in light element/ferromagnet heterostructures has become of great interest for spintronics. Here, we present a comparative study of the Rashba-type DMI in the h-BN/Co and graphene/Co heterostructures using first-principles calculations. Unexpectedly, they show opposite trend as a function of Co thickness. With the increase of Co thickness, the DMI coefficient of h-BN/Co first increases gradually and then saturates at around 1.1 meV for thick Co layers, whereas the DMI at graphene/Co interfaces first decreases and then stabilizes at about 0.1 meV for large Co thickness. For thick Co layers, the DMI strength of h-BN/Co is one order of magnitude larger than that of graphene/Co. The origin of this discrepancy is attributed to the different contribution from the hybridization between dz² and dxz orbitals of the interfacial Co layer to the DMI energy source. These results give deeper insight into microscopic formation of DMI and should help to optimize the material selection for future spin-orbitronic devices.
[1] H. X. Yang et al., Nat. Mater. 17, 605 (2018).
[2] F. Ajejas et al., Nano Lett. 18, 5364 (2018).