  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.
