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 (${\mathrm{Sr}}_{1\text{−}x}{\mathrm{Ba}}_x\mathrm{Ru}{\mathrm{O}}_3$ with $0\le x\le 0.7$). 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 ${180}^{\circ }$), resulting in the maximum Curie temperature and an extinction of $\mathrm{Ru}{\mathrm{O}}_6$ rotational distortions at $x\approx 0.20$. For $x\le 0.2$, 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 $\left(x>0.2\right)$ gradually enhances the tetragonal-type distortion, resulting in the tuning of $\mathrm{Ru}\text{−}4d$ orbital occupancy and suppression of ferromagnetism. Our results demonstrate that isovalent substitution of the $A\text{−}\mathrm{site}$ cations significantly and controllably impacts both electronic and magnetic properties of perovskite oxides.

• Received 28 November 2022
• Revised 29 January 2023
• Accepted 17 March 2023

DOI:https://doi.org/10.1103/PhysRevB.107.144405