Surface magnetism of the carbon foam: An ab-initio theoretical study

By means of ab-initio calculations, we study the surface magnetism of carbon foam, a carbon allotrope constructed by both the sp2 and sp3 hybridized carbon atoms. It is found that the sp3-terminated surface and sp2-terminated surface with hydrogen saturation (sp2H) have the antiferromagnetic and ferromagnetic ground states, respectively. And the corresponding phase transition temperatures of these two surfaces are estimated to exceed 100 K. In addition, the magnetic moment of the sp2H surface can be effectively modulated by strain. More interestingly, at the level of generalized gradient approximation, as the lattice are stretched, a bulk bandgap will open. And in such a bandgap, the sp2H surface states can form spin polarized Dirac cones at K(K′) point. Thus, in the vicinity of the Fermi level, only the electron with a specific spin behaves like a Dirac Fermion.