Abstract
Oxygen vacancies can be of utmost importance for improving or deteriorating physical properties of oxide materials. Here, we studied from first-principles the electronic and magnetic properties of oxygen vacancies in the double perovskite Sr2FeMoO6 (SFMO). We show that oxygen vacancies can increase the Curie temperature in SFMO, although the total magnetic moment is reduced at the same time. We found also that the experimentally observed valence change of the Fe ions from 3+ to 2+ in the x-ray magnetic circular dichroism (XMCD) measurements is better explained by oxygen vacancies than by the assumed mixed valence state. The agreement of the calculated x-ray absorption spectra and XMCD results with experimental data is considerably improved by inclusion of oxygen vacancies.
Highlights
S Supplementary material for this article is available online (Some figures may appear in colour only in the online journal)
We show that oxygen vacancies can increase the Curie temperature in SFMO, the total magnetic moment is reduced at the same time
We found that the experimentally observed valence change of the Fe ions from 3+ to 2+ in the x-ray magnetic circular dichroism (XMCD) measurements is better explained by oxygen vacancies than by the assumed mixed valence state
Summary
The physical origin of the magnetoresistance in SFMO is half-metallicity [18], i.e. the material is an insulator in one of the spin channels, but a metal in the other This leads to a complete spin polarization at the Fermi level, which immediately suggests their applica tion as a source of spin polarized charge carriers in spintronic devices. Therein, SFMO will be used mainly as a thin film, and many attempts were made to grown high quality films [16, 17, 19,20,21] All these films yield a reduced Curie temper ature, which is up to 80 K smaller than for bulk samples [16, 17]. Even for bulk SFMO the theoretical magnetic moment of 4 μB was rarely experimentally observed [8] Such variations were attributed to lattice defects like grain boundaries or point defects.
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