Defect-Induced Magnetism in Graphene: An Ab Initio Study

Graphene is an amazing two-dimensional system with exceptional physical and chemical properties. Potential applications in quantum information processing have been proposed for C-based materials, in particular for graphene system, where electron spin is a promising candidate for a solid-state qubit. The preservation of long spin coherence time is the fundamental feature to get for efficient working spin-qubit system. Despite graphene environment seems to suit the goal, defects in the structure, interactions with impurities and edge states can be a source of alteration of quantum information, since they could enhance the decoherence effects. The present work is a computational analysis of defective systems. It focuses on the investigations of various prototypical defect states (vacancies) and impurities interacting with graphene surface (hydrogen, boron, nitrogen, and oxygen) by means of density functional theory (DFT). We provide a preliminary study about the effects of these interactions. Vacancy-type defects give rise to a breaking of graphene symmetry, promoting a localized state with a magnetic moment whose magnitude is concentration-dependent. Hydrogen promotes a locally hybridization of the structure providing a localized magnetic moment and giving rise to an enhancement of spin-orbit interaction of about three orders of magnitude, showing the impact of hydrogen on spin-relaxation time. Among boron, nitrogen, and oxygen, the work has shown that the only one which returns a magnetic ground state is nitrogen. Boron provides an n-doping of defective-graphene. Oxygen leads to a hybridization of carbon atoms bonding, but its electronic structure does not allow a magnetic system. In the particular case of a bridge-like adsorption site. Among the different configurations for the adsorption sites, the bridge-site is energetically the most stable one, showing as in the other configurations for nitrogen, a magnetic system. Nitrogen adatoms develop a magnetic order (at zero temperature) which is always ferromagnetic independently from the distance between two adjacent nitrogen atoms.