Oxygen-vacancy tuning of magnetism in SrTi${}_{0.75}$Fe${}_{0.125}$Co${}_{0.125}$O${}_{3-\delta }$ perovskite

Abstract

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.

11 pages, 10 figures