We report a comprehensive experimental investigation of the magnetic ground state in ${\mathrm{ZnCoP}}_2{\mathrm{O}}_7$, where ${\mathrm{Co}}^{2+}$ ions in octahedral coordination realize an effective $J_{\mathrm{eff}}=1/2$ state and form a quasi-one-dimensional zigzag lattice comprising alternating edge-shared dimers. This unique magnetic geometry promotes strong frustration through competing nearest-neighbor and next-nearest-neighbor exchange interactions. Using complementary $\mathrm{dc}$ and $\mathrm{ac}$ magnetic susceptibility, specific heat, inelastic neutron scattering (INS), muon spin relaxation ($\mu \mathrm{SR}$) measurements, and ${}^{31}\mathrm{P}$ nuclear magnetic resonance (NMR) experiments, we find no evidence of long-range magnetic order down to $\simeq 30\mathrm{mK}$, despite sizable antiferromagnetic interactions. Instead, persistent low-temperature spin dynamics, broad diffuse magnetic scattering, and the absence of sharp dispersive magnetic excitations reveal a highly correlated dynamic ground state. These observations identify ${\mathrm{ZnCoP}}_2{\mathrm{O}}_7$ as a rare example of a quasi-one-dimensional, spin-orbit-coupled quantum magnet exhibiting key experimental signatures consistent with a spin liquid ground state. The most likely microscopic origin of this spin liquid state is the combined effect of frustrated competing exchange interactions, low dimensionality, and spin-orbit entanglement.

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• Crystal-field excitations
• Magnetic anisotropy
• Magnetic coupling
• Magnetic interactions
• Magnetic susceptibility
• Quantum spin liquid
• Spin-orbit coupling
• Structural properties
• Antiferromagnets