Ferromagnetism in nitrogen-doped BaO: a self-interaction corrected DFT study.

The nature of isolated nitrogen-dopants in bulk BaO (N-BaO) and their magnetic interaction have been investigated by means of density functional theory calculations based on hybrid, self-interaction corrected functionals. A thermodynamic analysis shows that N is preferably incorporated into interstitial sites. Only at very high temperatures and under oxygen poor-conditions the formation of N dopants substitutional to O is preferred. The spin density is rather localized in both cases, as proven by the calculation of the hyperfine coupling constants of the electron spin with the nuclear spin of nitrogen. The magnetic interaction of two N defects in various configurations has been considered as a function of their distance. Different behaviors have been observed, depending on the position of the N defects and on the nature of the dominating magnetic mechanism. In any case, the computed Curie temperature is below room temperature, suggesting that RT ferromagnetism cannot be attained for this kind of doping in BaO. Finally, the interplay of oxygen vacancies with the N dopants has been studied. The inclusion of nitrogen has the effect of drastically reducing the cost to create oxygen vacancies. These in turn quench the magnetic moment of N-dopants, contributing to reducing the concentration of magnetic impurities.