Examination of the magnetic interactions between divacant Fe dimers in graphene*

In this study, we investigate the isolated magnetic interactions between two identical Fe atoms substituted into graphene. Using density functional theory, we simulated the electronic and magnetic properties for a supercell of graphene with variably-spaced iron atoms in the divacant configuration. Overall, we find that the exchange interaction between the two Fe atoms fluctuates from ferromagnetic to antiferromagnetic as a function of the spatial distance in the armchair direction. Given the induced magnetic moment and increased density of states at the Fermi level by the surrounding carbon atoms, we conclude that the exchange interactions between the Fe atoms can be characterized by an RKKY-like interaction. Furthermore, we examined the same interactions for Fe atoms along the zig-zag direction in graphene and find no evidence for an RKKY interaction as this system shows standard superexchange between the transition-metal impurities. Therefore, we determine that Fe-substituted graphene produces a directional-dependent spin interaction, which may provide stability to spintronic and multifunctional devices and applications for graphene.