Weak In-Plane Ferromagnetism and Electronic Nematicity in the Distorted Triple-Q Magnetic Phase of Co_1/3TaS₂

An intercalated transition-metal dichalcogenide ${\mathrm{Co}}_{1/3}{\mathrm{TaS}}_2$ hosts a triple-Q (3Q) noncoplanar antiferromagnetic state that co-exists with $Z_3$ electronic nematicity, indicating broken threefold rotational symmetry. This nematicity exhibits versatile field- and strain-tunability, making it promising for spintronics applications. However, its microscopic connection to magnetism has remained unclear. Here, we report rotational hysteresis observed in both magnetoresistance and magnetic torque, revealing strongly pinned in-plane weak ferromagnetic moments in the triple-Q phase and the magnetism-driven nature of the co-existing nematicity. In particular, when fields are rotated within a narrow angular range to restrict magnetization reversal, we observe additional hysteresis loops. This hysteresis can be well explained by domain repopulation, further supported by our theoretical simulations based on the spin Hamiltonian of ${\mathrm{Co}}_{1/3}{\mathrm{TaS}}_2$ . These results demonstrate that the weak in-plane ferromagnetic moment offers an additional handle on the spin-driven electronic nematicity, providing a microscopic picture of the field-tunable electronic responses in the 3Q state of ${\mathrm{Co}}_{1/3}{\mathrm{TaS}}_2$ .