Oxygen-vacancy tuning of magnetism in SrTi 0.75 Fe 0.125 Co 0.125 O 3 -δ perovskite

We use density functional theory to calculate the structure, band-gap, and magnetic properties of oxygen-deficient ${\mathrm{SrTi}}_{1\ensuremath{-}x\ensuremath{-}y}{\mathrm{Fe}}_{x}{\mathrm{Co}}_{y}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ with $x=y=0.125$ and $\ensuremath{\delta}={0,0.125,0.25}$. 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, on 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 $\ensuremath{\delta}=0.125$. This qualitatively mimics the previously reported magnetization measured for ${\mathrm{SrTiFeO}}_{3\ensuremath{-}\ensuremath{\delta}}$, which was maximum at an intermediate deposition pressure of oxygen.