Evolution of graphene mediated magnetic coupling between Fe-chains

First principles electronic structure studies on the structure, stability, and magnetic coupling of Fe-chains at the zigzag edges of graphene ribbons have been carried out within a gradient-corrected density functional formalism. Our studies indicate that Fe sites in the chain undergo a structural rearrangement into Fe–Fe pairs. The Fe sites within a given chain are ferromagnetically aligned, but chains across the ribbon have an antiferromagnetic ground state. Studies on ribbons of increasing width show that the energy difference between magnetic states decreases with increasing width attaining a value of only 8.9 meV per unit cell for chains separated by 2 nm.