Large Magnetic Anisotropy in OsIr Dimer Anchored in Defective Graphene.

Single-atom magnets represent the ultimate limit of the magnetic data storage. Identifying substrates anchoring atom-size magnets firmly and, thus, preventing their diffusion and large magnetic anisotropy has been in the centre of intense research efforts for a long time. By using density functional theory (DFT) we show that the binding of transition metal (TM) atoms in defect sites in the graphene lattice: Single vacancy (SV) and double vacancy (DV), both pristine and decorated by pyridinic nitrogen atoms (NSV and NDV), is energetically more favourable than away from the centre of defects, which could be used for engineering the position of TMs with atomic precision. Relativistic calculations revealed magnetic anisotropy energy (MAE) of ~10 meV for Ir@NSV with an easy axis parallel to the graphene plane. MAE can be remarkably boosted to 50 meV for OsIr@NSV with the easy axis perpendicular to the graphene plane, which paves the way to the storage density of ~490 Tb/inch2with the blocking temperature of 14 K assuming the relaxation time of 10 years. Magnetic anisotropy is discussed based on the relativistic electronic structures. The influence of an orbital-dependent on-site Coulomb repulsionUand a non-local correlation functional optB86b-vdW on MAE is also discussed.