Magnetism in Disordered Graphene and Irradiated Graphite

The magnetic properties of disordered graphene and irradiated graphite are systematically studied using a combination of mean-field Hubbard model and first-principles calculations. By considering large-scale disordered models of graphene, I conclude that only single-atom defects can induce ferromagnetism in graphene-based materials. The preserved stacking order of graphene layers is shown to be another necessary condition for achieving a finite net magnetic moment of irradiated graphite. Ab initio calculations of hydrogen binding and diffusion and of interstitial-vacancy recombination further confirm the crucial role of stacking order in $\pi$-electron ferromagnetism of proton-bombarded graphite.

Figure 1

Average magnetic moments of carbon atoms in $A$ and $B$ sublattices of graphene as a function of vacancy concentration for different $U/t$ values. The vacancies are either (a) distributed equally among sublattices or (b) belong to sublattice $B$ only. (c) Spin density distribution in a representative configuration with vacancy defects ($x=0.03$) in sublattices $A$ (▴) and $B$ (▾).

Figure 2

(a) Average magnetic moments of carbon atoms in $A$ and $B$ sublattices of graphene as a function of bond dilution for different $U/t$ values and (b) spin density distribution in a representative configuration ($x=0.10$; $U/t=1.33$).

Figure 3

(a) Inequivalent carbon atoms ($A$ and $B$) in graphite. (b) Possible pathways for the diffusion of chemisorbed hydrogen in the $ab$ plane of graphite. (c) Relative energies of the potential energy surface minima and transition states for the diffusion of chemisorbed hydrogen in graphite.