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Although barium ferrate is known to accommodate a range of oxygen stoichiometries, which give rise to distinct magnetic properties, the mechanism underlying this coupling is not clearly understood. In order to address this issue, the electronic and magnetic properties of pseudocubic BaFeO3−δ with 0 ≤δ≤ 0.5 were studied using density functional theory. The present results attest the influence of the oxygen content on the magnetic order: for high oxygen content, the magnetic interactions are predominantly ferromagnetic whereas for oxygen deficient stoichiometries the antiferromagnetic interactions prevail. The threshold separating the two regimes is determined by the competition between double-exchange and super-exchange interactions which sensitively depend on the occupation of the oxygen band. Due to the high electronic affinity of the Fe ions in this compound, which results in a negative ligand to metal charge transfer energy, the system behaves as self-doped and the oxygen content has little effect on the 3d Fe band occupation, affecting instead the occupation of the anionic band.

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