Tuning structural, transport, and magnetic properties of epitaxial SrRuO3 through Ba substitution

The perovskite ruthenates ($A\mathrm{Ru}{\mathrm{O}}_{3}, A=\mathrm{Ca}$, Ba, or Sr) exhibit unique properties owing to a subtle interplay of crystal structure and electronic-spin degrees of freedom. Here, we demonstrate an intriguing continuous tuning of crystal symmetry from orthorhombic to tetragonal (no octahedral rotations) phases in epitaxial $\mathrm{SrRu}{\mathrm{O}}_{3}$ achieved via Ba substitution (${\mathrm{Sr}}_{1\text{\ensuremath{-}}x}{\mathrm{Ba}}_{x}\mathrm{Ru}{\mathrm{O}}_{3}$ with $0\ensuremath{\le}x\ensuremath{\le}0.7$). An initial Ba substitution to $\mathrm{SrRu}{\mathrm{O}}_{3}$ not only changes the ferromagnetic properties, but also tunes the perpendicular magnetic anisotropy via flattening the Ru--O--Ru bond angle (to ${180}^{\ensuremath{\circ}}$), resulting in the maximum Curie temperature and an extinction of $\mathrm{Ru}{\mathrm{O}}_{6}$ rotational distortions at $x\ensuremath{\approx}0.20$. For $x\ensuremath{\le}0.2$, the reduction of $\mathrm{Ru}{\mathrm{O}}_{6}$ octahedral rotational distortion dominantly enhances the ferromagnetism in the system, though competing with the effect of the $\mathrm{Ru}{\mathrm{O}}_{6}$ tetragonal distortion. Further increasing Ba substitution $(x>0.2)$ gradually enhances the tetragonal-type distortion, resulting in the tuning of $\mathrm{Ru}\text{\ensuremath{-}}4d$ orbital occupancy and suppression of ferromagnetism. Our results demonstrate that isovalent substitution of the $A\text{\ensuremath{-}}\mathrm{site}$ cations significantly and controllably impacts both electronic and magnetic properties of perovskite oxides.