We report a ${\mathrm{La}}_2{\mathrm{CuO}}_4$-like interlayer antiferromagnetic order in ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ films with large orthorhombic distortion $(>1.5\%)$. The biaxial lattice strain in epitaxial heterostructures of ${\mathrm{Sr}}_2{\mathrm{IrO}}_4/{\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ lowers the crystal symmetry of ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ from tetragonal ($C_4$) to orthorhombic ($C_2$), guiding the Ir $5d J_{\mathrm{eff}}=1/2$ pseudospin moment parallel to the elongated $b$ axis via magnetic anisotropy. From resonant x-ray scattering experiments, we observed an antiferromagnetic order in the orthorhombic ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ film whose interlayer stacking pattern is inverted from that of the tetragonal ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ crystal. This interlayer stacking is similar to that of the orthorhombic ${\mathrm{La}}_2{\mathrm{CuO}}_4$, implying that the asymmetric interlayer exchange interactions between $a$ and $b$ directions exceed the anisotropic interlayer pseudodipolar interaction. Our result suggests that strain-induced distortion can provide a delicate knob for tuning the long-range magnetic order in quasi-two-dimensional systems by evoking the competition between the interlayer exchange coupling and the pseudodipolar interaction.

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• Antiferromagnetism
• Dipolar interaction
• Exchange interaction
• Antiferromagnets
• Thin films
• Laser ablation
• X-ray resonant magnetic scattering