A variety of exotic spin-orbital entangled magnetic ground states is expected in $4d$ transition-metal oxides (TMOs) featuring an ideal octahedral environment and active $t_{2\mathrm{g}}$ orbitals, due to the comparable strength of spin-orbit coupling (SOC), superexchange interaction, and Hund's coupling ($J_{\mathrm{H}}$). However, for the TMOs with a $d^3$ electronic configuration, orbital degrees of freedom are supposed to be quenched and SOC is generally expected to play no role in determining the magnetic ground state. The present study, through comprehensive investigations of the structural and physical properties (using neutron diffraction, dc as well as ac magnetization techniques, electron-spin-resonance study, and specific-heat analysis), shows a canted antiferromagnetic ground state for $\mathrm{C}{\mathrm{a}}_3\mathrm{LiRu}{\mathrm{O}}_6$, having $\mathrm{R}{\mathrm{u}}^{5+}$ with $4d^3$ electronic configuration in an octahedral crystal field. In the magnetic ground state, the moments are predominantly aligned along the crystallographic $a$ axis. The dc magnetization study shows strong anisotropy and short-range correlations (SROs) persisting above the transition temperature. The SRO above the transition temperature is also confirmed from the specific-heat study. Our ab initio calculations corroborate these experimental observations by demonstrating the critical roles of SOC and strong hybridization between the Ru $d$ and O $p$ states in determining spin canting, and the 3D nature of magnetic exchange interactions.

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• Exchange interaction
• Magnetism
• Spin-orbit coupling
• Density functional calculations