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Register a new userOxygen-vacancy tuning of magnetism in SrTi$_{0.75}$Fe$_{0.125}$Co$_{0.125}$O$_{3-delta}$ perovskite
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Added by
Juan Manuel Florez Dr.
Publication date
2019
fields
Physics
and research's language is
English
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We use density functional theory to calculate the structure, band-gap and magnetic properties of oxygen-deficient SrTi$_{1-x-y}$Fe$_x$Co$_y$O$_{3-delta}$ with x = y = 0.125 and ${delta}$ = (0,0.125,0.25). The valence and the high or low spin-states of the Co and Fe ions, as well as the lattice distortion and the band-gap, depend on the oxygen deficiency, the locations of the vacancies, and on the direction of the Fe-Co axis. A charge redistribution that resembles a self-regulatory response lies behind the valence spin-state changes. Ferromagnetism dominates, and both the magnetization and the band gap are greatest at ${delta}$ = 0.125. This qualitatively mimics the previously reported magnetization measured for SrTiFeO$_{3-delta}$, which was maximum at an intermediate deposition pressure of oxygen.
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We use density functional theory (DFT) calculations to show that oxygen vacancies ($v_mathrm{O}$) induce noncentrosymmetric polar structures in SrTi$_{0.75}$Fe$_{0.125}$Co$_{0.125}$O$_{3-delta}$ (STFC) with $delta = {0.125, 0.25}$, enhance the magnetic moment and give rise to large changes in the electric polarization $vertDelta Pvert$. Variations of $delta$ or oxygen vacancy migration for a given deficiency are shown to be effective mechanisms to tune the ferroic order parameters, with the former yielding $vertDelta Pvert$ values up to $sim{8mu}$C/c$m^{2}$ while the latter yields $vertDelta Pvert$ up to $sim{23mu}$C/c$m^{2}$. The underlying mechanism is the differentiated self-regulatory-like ferroic response of Fe and Co through the (Fe/Co)-$v_mathrm{O}$ and Fe-$v_mathrm{O}$-Co interactions, which drive B-site off-centering, bending of O$_{4,5}$ incomplete octahedra and B-$v_mathrm{O}$ aligned distortions, all with characteristic charge redistributions. Our results capture characteristics observed in the end-members of the series SrTi(Co,Fe)O$_{3}$, and predict multiferroic behavior that could also be present in other ABO$_{3-delta}$ magnetic oxides.
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