Impact of oxygen doping and oxidation state of iron on the electronic and magnetic properties ofBaFeO3−δ

Abstract

We studied structural, electronic and magnetic properties of a cubic perovskite BaFeO 3−δ (0 ≤ δ ≤ 0.5) within the density functional theory using a generalized gradient approximation and a GGA+U method. According to our calculations, BaFeO3 in its stoichiometric cubic structure should be half-metallic and strongly ferromagnetic, with extremely high Curie temperature (TC ) of 700 -900 K. However, a such estimate of TC disagrees with all available experiments, which report that TC of the BaFeO3 and undoped BaFeO 3−δ films varies between 111 K and 235 K or, alternatively, that no ferromagnetic order was detected there. Fitting the calculated x-ray magnetic circular dichroism spectra to the experimental features seen for BaFeO3, we concluded that the presence of oxygen vacancies in our model enables a good agreement. Thus, the relatively low TC measured in BaFeO3 can be explained by oxygen vacancies intrinsically presented in the material. Since iron species near the O vacancy change their oxidation state from 4+ to 3+, the interaction between Fe 4+ and Fe 3+ , which is antiferromagnetic, weakens the effective magnetic interaction in the system, which is predominantly ferromagnetic. With increasing δ in BaFeO 3−δ , its TC decreases down to the critical value when the magnetic order becomes antiferromagnetic. Our calculations of the electronic structure of BaFeO 3−δ illustrate how the ferromagnetism originates and also how one can keep this cubic perovskite robustly ferromagnetic far above the room temperature.

Strain induced Jahn-Teller distortions in BaFeO3 : A first-principles study

“…Thus, we confirm that the breathing distortion is unlikely to be present in BaFeO 3 . Our finding agrees with the recent work of Maznichenko et al 63 , who used DFT and XAS, XMCD experiments and they concluded that the oxidation of Fe in BaFeO 3 is +4 and it can change from +4 to +3 only if oxygen vacancies are present.…”

Improper ferroelectricity at antiferromagnetic domain walls of perovskite oxides

“…The plane-wave cutoff is set to 550 eV. Moreover, the strong on-site Coulomb interaction on the Fe 3d orbitals is considered by including a Hubbard U correction [25] of 3 eV for Fe [26,27] because this value of U provides rather accurate results for a range of binary and ternary Fe oxides [28,29]. We checked that other reasonable U values yield qualitatively similar results.…”

Dynamic stabilization of perovskites at elevated temperatures: A comparison between cubic BaFeO$_{\textbf{3}}$ and vacancy-ordered monoclinic BaFeO$_{\textbf{2.67}}$

“…Further, a magnetic transition to the FM state was observed experimentally at 111 K [23]. The FM state was also shown to be energetically the most stable within calculations with collinear spin alignment [32][33][34]. For the vacancy-ordered monoclinic BaFeO 2.67 structure, experimental and ab initio results show agreement on a G-AFM ordering [7].…”