Orientation control of oxygen vacancy channels in brownmillerite SrFeO2.5

Abstract

The geometrical control of oxygen vacancy channels (OVCs) and their orientation in brownmillerite (BM) structures provide a platform for tailoring the physical properties. The growth with different OVCs orientation implies a huge change in lattices that limit the epitaxial growth. Here we achieve epitaxial growth of $\mathrm{SrFe}{\mathrm{O}}_{2.5}$ ($\mathrm{SF}{\mathrm{O}}_{2.5}$) films with horizontal or vertical OVCs, irrespective of the substrates of (001) $\mathrm{SrTi}{\mathrm{O}}_{3}, \mathrm{L}{\mathrm{a}}_{0.3}\mathrm{S}{\mathrm{r}}_{0.7}\mathrm{A}{\mathrm{l}}_{0.65}\mathrm{T}{\mathrm{a}}_{0.35}{\mathrm{O}}_{3}$, and $\mathrm{LaAl}{\mathrm{O}}_{3}$. For vertical OVCs, the substrate mismatch is overcome by the topotactic phase transition of $\mathrm{SrFe}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ at the film/substrate interface, whereas the epitaxy with horizontal OVCs is achieved simply by low oxygen pressure growth. It is found that the antiferromagnetic axes of the prepared films are intimately associated with crystal orientation that can be changed by controlling the OVCs direction, while the (ferro)magnetic anisotropy is also observed accompanied by more robust magnetization in the direction perpendicular to the OVCs, where the magnetization arises from the canted moments. Horizontal and vertical OVCs scenarios are also achieved in $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}/\mathrm{SF}{\mathrm{O}}_{2.5}$ bilayer samples in a controllable manner, which show ferromagnetic coupling and decoupling, respectively. Our findings not only add a different dimension for the epitaxial growth of films on a wide range of substrates but also demonstrates the use of OVCs for tailoring physical properties of oxides.