Graphene-Supported Atom-Sized Magnets for Data Storage: What Can We Learn from First-Principles Calculations?

Doping the graphene lattice with transition metal (TM) atoms has been identified as an effective strategy for obtaining high magnetic anisotropy energy (MAE), preventing thermally induced reorientation of magnetic moments between the easy and hard magnetization axes. Lattice imperfections such as atomic vacancies can anchor TM atoms or their clusters, preventing them from diffusing and agglomerating on the surface, ultimately allowing high MAEs of 170 meV for an OsPd dimer bound to a single nitrogen-decorated vacancy (NSV) in the graphene lattice. Importantly, the lighter TM dimers, FeMn bound to two separate double-vacancy (DV) defects, can also exhibit a significant MAE of 120 meV when interacting with each other through the graphene lattice. The presence of Mn impurities associated with DV defects in the graphene lattice has been confirmed experimentally and can form anchors for the formation of FeMn dimers. For practical applications of graphene-supported magnetic dimers, the carbon sheet must be deposited on a solid support. A properly selected substrate can, to a large extent, allow for the preservation of a large MAE of dimers.