Interface engineering of metal-oxygen bonds as a new route for exploring functional properties of transition metal oxides

Metal-oxygen bonds in transition-metal oxides are responsible for a broad spectrum of functional properties, and atomic-level control of the bonds is a key for developing future oxide-based electronics. Artificial heterostructures with chemically abrupt interfaces consisting of dissimilar oxides have provided a good platform for engineering novel bonding geometries that could lead to emergent phenomena not seen in bulk oxides. Here we show that the Ru-O bonds (or oxygen coordination environments) of a perovskite, SrRuO$_{\mathrm{3}}$, can be controlled by heterostructuring SrRuO$_{\mathrm{3}}$ with a thin (0--4 monolayers thick) Ca$_{\mathrm{0.5}}$Sr$_{\mathrm{0.5}}$TiO$_{\mathrm{3}}$ layer grown on GdScO$_{\mathrm{3}}$ substrates [1]. We found that a Ru-O-Ti bond angle characterizing the SrRuO$_{\mathrm{3}}$/Ca$_{\mathrm{0.5}}$Sr$_{\mathrm{0.5}}$TiO$_{\mathrm{3}}$ interface structure can be engineered by layer-by-layer control of the Ca$_{\mathrm{0.5}}$Sr$_{\mathrm{0.5}}$TiO$_{\mathrm{3}}$ layer thickness, and that the engineered Ru-O-Ti bond angle not only stabilizes a Ru-O-Ru bond angle never seen in bulk SrRuO$_{\mathrm{3}}$ but also tunes the magnetic anisotropy in the entire SrRuO$_{\mathrm{3}}$ layer. The results demonstrate that interface engineering of the metal-oxygen bonds is a good way to control additional degrees of freedom in designing functional oxide heterostructures. [1] D. Kan et al Nature Materials 15, 432 (2016).