We report on a comprehensive investigation of the effects of strain and film thickness on the structural and magnetic properties of epitaxial thin films of the prototypal $J_{\mathrm{eff}}=1/2$ compound ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ by advanced x-ray scattering. We find that the ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ thin films can be grown fully strained up to a thickness of 108 nm. By using x-ray resonant scattering, we show that the out-of-plane magnetic correlation length is strongly dependent on the thin film thickness, but independent of the strain state of the thin films. This can be used as a finely tuned dial to adjust the out-of-plane magnetic correlation length and transform the magnetic anisotropy from two-dimensional to three-dimensional behavior by incrementing film thickness. These results provide a clearer picture for the systematic control of the magnetic degrees of freedom in epitaxial thin films of ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ and bring to light the potential for a rich playground to explore the physics of $5d$ transition-metal compounds.

• Received 22 September 2020
• Revised 4 November 2020
• Accepted 4 November 2020

DOI:https://doi.org/10.1103/PhysRevB.102.214402