${\mathrm{RuO}}_2$, proposed as a potential altermagnet, is expected to serve as a new-generation spintronic material enabling precise control of spin transport. However, the existence of magnetic order in ${\mathrm{RuO}}_2$ has recently been widely questioned. Here, based on first-principles calculations, we systematically investigate the magnetic order in ${\mathrm{RuO}}_2$ under epitaxial strain. We find that a modest global strain can drive ${\mathrm{RuO}}_2$ from a nonmagnetic state to an antiferromagnetic state. Furthermore, near the strain-induced magnetic critical point, a modest local distortion can stabilize a spin-density-wave state over the antiferromagnetic state, with an energy difference on the order of $10-100\mu \text{eV}$ and a characteristic wavelength of about 7–10 nm. Our study provides a unified microscopic picture for the experimental controversy regarding altermagnetism in ${\mathrm{RuO}}_2$, and highlights the key roles of global strain and local distortion in tuning ${\mathrm{RuO}}_2$ magnetism and spin transport.

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• Distortions & defects
• Epitaxial strain
• Magnetic order
• Spin density waves
• Spin state transition
• Altermagnets
• Transition metal oxides
• Density functional calculations
• Strain engineering