Exploring materials with unconventional spin transport properties and manipulating magnetic moments are core focuses in spintronics. Herein, we report the crystallographic orientation-dependent field-free switching of perpendicular magnetization in $\mathrm{STO}//{\mathrm{RuO}}_2(100)/[\mathrm{C}\mathrm{o}/\mathrm{Pt}{]}_2$ heterostructure, driven by spin splitting torque of ${\mathrm{RuO}}_2$. Unlike ${\mathrm{RuO}}_2(101)$-based systems, the $\mathrm{STO}//{\mathrm{RuO}}_2(100)/[\mathrm{C}\mathrm{o}/\mathrm{Pt}{]}_2$ eliminates confounding factors including crystal structural effects and perpendicular magnetic moment tilting, which allows us to attribute field-free switching exclusively to ${\mathrm{RuO}}_2$ antiferromagnetic order. When the Néel vector in $\mathrm{STO}//{\mathrm{RuO}}_2(100)$ deviates from the [001] easy axis and acquires an out-of-plane component, the anisotropic spin splitting effect generates out-of-plane spin polarization spin current, which provides damping-like torque to drive field-free switching at a critical current density of approximately $1.6\times {10}^7\text{A}/{\text{cm}}^2$. Complemented by temperature-dependent oscillating exchange bias that reverses sign at 90 K, our results unambiguously confirm the antiferromagnetic order of ${\mathrm{RuO}}_2$ in the heterostructure. This work offers evidence for spin splitting torque in ${\mathrm{RuO}}_2$-based heterostructures, deepens the understanding of altermagnetic spin transport, and paves the way for the development of field-free spintronic devices.

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• Magnetization switching
• Spin current
• Spin polarization
• Spin-orbit torque
• Altermagnets
• Antiferromagnets
• Magnetic multilayers
• Magnetization measurements