title: Crafting ferromagnetism in Mn-doped MgO surfaces with p-type defects.
abstract: We have employed first-principles calculations based on density functional theory (DFT) to investigate the underlying physics of unusual magnetism in Mn-doped MgO surface. We have studied two distinct scenarios. In the first one, two Mn atoms are substitutionally added to the surface, occupying the Mg sites. Both are stabilized in the Mn[Formula: see text] valence state carrying a local moment of 4.3 [Formula: see text] having a high-spin configuration. The magnetic interaction between the local moments display a very short-ranged characteristic, decaying very quickly with distance, and having antiferromagnetic ordering lower in energy. The energetics analysis also indicates that the Mn ions prefer to stay close to each other with an oxygen atom bridging the local interaction. In the second scenario, we started exploring the effect of native defects on the magnetism by crafting both Mg and O vacancies, which are p- and n-type defects, respectively. It is found that the electrons and holes affect the magnetic interaction between Mn ions in a totally different manner. The n-type defect leads to very similar magnetism, with the AFM configuration being energetically preferred. However, in the presence of Mg vacancy, the situation is quite different. The Mn atoms are further oxidized, giving rise to mixed Mn(d) ionic states. As a consequence, the Mn atoms couple ferromagnetically, when placed in the close configuration, and the obtained electronic structure is coherent with the double-exchange type of magnetic interaction. To guarantee the robustness of our results, we have benchmarked our calculations with three distinct theory levels, namely DFT-GGA, DFT-GGA+U and DFT-hybrid functionals. On the surface, the Mg vacancy displays lower formation energy occurring at higher concentrations. Therefore, our model systems can be the basis to explain a number of controversial results regarding transition metal doped oxides.
authors.affiliation: Condensed Matter Theory Group, Materials Theory Division, Department of Physics and Astronomy, Uppsala University, PO Box 530, S75121, Uppsala, Sweden.
authors.forename: Puspamitra
authors.initials: P
authors.lastname: Panigrahi
authors.affiliation: Condensed Matter Theory Group, Materials Theory Division, Department of Physics and Astronomy, Uppsala University, PO Box 530, S75121, Uppsala, Sweden.
authors.forename: C Moyses
authors.initials: CM
authors.lastname: Araujo
authors.affiliation: Condensed Matter Theory Group, Materials Theory Division, Department of Physics and Astronomy, Uppsala University, PO Box 530, S75121, Uppsala, Sweden.
authors.forename: Tanveer
authors.initials: T
authors.lastname: Hussen
authors.affiliation: Condensed Matter Theory Group, Materials Theory Division, Department of Physics and Astronomy, Uppsala University, PO Box 530, S75121, Uppsala, Sweden; Applied Materials Physics, Departments of Materials and Engineering, Royal Institute of Technology (KTH), S-10044, Stockholm, Sweden.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Ahuja
keywords: dilute magnetic semiconductor; double exchange interaction; ferromagnetism; hole induced