In this work, a first-principles study of the energetic and magnetic properties of V-doped MgO is presented, where both the bulk and (001) surface were investigated. It is found that V assumes a high-spin state with a local moment of about $3{\mu }_{\text{B}}$. In the bulk, the interaction between these local moments is very short ranged and the antiferromagnetic (AFM) ordering is energetically more favorable. The formation of ${\text{V-V}}_{\text{Mg}}\text{-V}$ defect clusters is found to weaken the antiferromagnetic coupling in bulk MgO, degenerating the AFM and ferromagnetic state. However, these clusters are high in energy and will not form at equilibrium conditions. By employing the $\text{GGA}+U$ approach, with $U=5\text{eV}$, the $\text{V}3d$ states on the (001) surface are shifted below the Fermi level, and a reasonable surface geometry was achieved. A calculation with the hybrid HSE03 functional, contradicts the $\text{GGA}+U$ results, indicating that the V-MgO surface should be metallic at this concentration. From the energetics it is concluded that, at the modeled concentration, ${\text{V}}_x{\text{O}}_y$ phases will limit the solubility of V in MgO at equilibrium conditions, which is in agreement with previous experimental findings. In order to achieve higher concentrations of V, an off-equilibrium synthesis method is needed. Finally, we find that the formation energy of V at the surface is considerably higher than in the bulk and V is thus expected to diffuse from the surface into the bulk of MgO.

• Received 7 July 2009

DOI:https://doi.org/10.1103/PhysRevB.82.134406