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Sökning: swepub > Johansson Börje > Refereegranskat > (2010-2011) > Rao K. Venkat

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1.
  • Araujo, C. Moysés, et al. (författare)
  • Room temperature ferromagnetism in pristine MgO thin films
  • 2010
  • Ingår i: Applied Physics Letters. - 0003-6951. ; 96:23
  • Tidskriftsartikel (refereegranskat)abstract
    • Robust ferromagnetic ordering at, and well above room temperature is observed in pure transparent MgO thin films (<170 nm thick) deposited by three different techniques. Careful study of the wide scan x-ray photoelectron spectroscopy rule out the possible presence of any magnetic contaminants. In the magnetron sputtered films, we observe magnetic phase transitions as a function of film thickness. The maximum saturation magnetization of 5.7 emu/cm(3) is measured on a 170 nm thick film. The films above 500 nm are found to be diamagnetic. Ab initio calculations suggest that the ferromagnetism is mediated by cation vacancies.
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2.
  • Århammar, Cecilia, et al. (författare)
  • Energetics and magnetic properties of V-doped MgO bulk and (001) surface : A GGA, GGA+U, and hybrid density functional study
  • 2010
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 82:13, s. 134406
  • Tidskriftsartikel (refereegranskat)abstract
    • 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(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 V-V-Mg-V defect clusters is found to weaken the antiferromagnetic coupling in bulk MgO, degenerating the AFM and ferro-magnetic state. However, these clusters are high in energy and will not form at equilibrium conditions. By employing the GGA+U approach, with U=5 eV, the 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 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, VxOy 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.
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