Spontaneous Hall conductivity has recently been reported in the triangular lattice antiferromagnet ${\mathrm{Co}}_{1/3}\mathrm{Ta}{\mathrm{S}}_2$ under a zero magnetic field. This phenomenon originates from the distinctive noncoplanar triple-Q magnetic ground state, possessing uniform real-space Berry curvature characterized by scalar spin chirality. We investigated the physical properties of ${\mathrm{Co}}_{1/3}\mathrm{Ta}{\mathrm{S}}_2$ by judiciously controlling the composition, revealing a drastic change in its bulk properties, even by slight variations in cobalt composition, despite the same crystal structure. For $0.299\le x\le 0.325, {\mathrm{Co}}_x\mathrm{Ta}{\mathrm{S}}_2$ keeps all the characteristics of the ground state consistent with the previous studies—two antiferromagnetic phase transitions at $T_{\mathrm{N}1}$ and $T_{\mathrm{N}2}$ ($<T_{\mathrm{N}1}$), a large spontaneous Hall conductivity $\left[{\sigma }_{xy}\left(\mathbf{H}=0\right)\right]$, and a weak ferromagnetic moment along the $c$ axis. However, samples with $x\ge 0.330$ exhibit distinct bulk properties, including the absence of both ${\sigma }_{xy}\left(\mathbf{H}=0\right)$ and the weak ferromagnetic moment. Our neutron diffraction data reveal that ${\mathrm{Co}}_x\mathrm{Ta}{\mathrm{S}}_2$ with $x\ge 0.330$ develops coplanar helical magnetic order with ${\mathbf{q}}_{\mathrm{m}1}=$(1/3, 0, 0). This is entirely different from what has been seen in $x\le 0.325$, explaining the observed composition dependence.

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• Frustrated magnetism
• Magnetic order
• Magnetism
• Antiferromagnets
• Chiral magnets
• Noncollinear magnets
• Single crystal materials
• Crystal growth
• Neutron diffraction