Long Range Ordering in Oxygen Doped SrCoO$_{x}$

Recent investigations have shown magnetic phase separation in polycrystalline samples of SrCoO$_{x} (2.5 \le x \le 3.0)$.\footnote{Xie et al. Appl. Phys. Lett 99, 052503 (2011)} As the samples are oxidized electrochemically, distinct ferromagnetic phases are formed at SrCoO$_{2.75}$ (T$_{C}$ = 165 K), SrCoO$_{2.88}$ (T$_{C}$ = 220 K), and SrCoO$_{3}$ (T$_{C}$ = 280 K). In the polycrystalline bulk samples, two magnetic phases are seen at oxygen concentrations between 2.875 and 3.0, always occurring in only a single structural phase. The distinct phases are also evident in epitaxial 100 nm films, but the mixed magnetic phase at intermediate concentrations is suppressed. The occurrence of separate magnetic phases at concentrations of 2.75 [3-1/4], 2.88 [3-1/8], and 3.0 imply an electronic ordering commensurate with the lattice. Using resonant x-ray diffraction in thin film samples, we have discovered the existence of a superlattice peak at (1/4, 1/4, 1/4), revealing a previously hidden order with a periodicity four times the basic perovskite cell in all directions.