Pressure-tuned suppression of noncoplanar order and emergence of a new magnetic ground state in Co_1/3TaS₂

  The van der Waals intercalated magnet Co_1/3TaS₂ exhibits two successive antiferromagnetic transitions at T_N1 = 38 K and T_N2 = 28.5 K, corresponding to a stripe-type single-Q and a noncoplanar triple-Q order that yields a topological Hall effect (THE) [1–3]. We investigated how these magnetic phases evolve under pressure up to 30 GPa using electrical transport, Hall effect, muon-spin rotation (µSR), and synchrotron X-ray diffraction. The THE is gradually suppressed and vanishes near 0.88 GPa, indicating the destabilization of the triple-Q state, while the stripe-type order persists up to 1.6 GPa. Above this pressure, a first-order-like transition occurs, accompanied by a resistivity upturn, negative magnetoresistance, and an anomaly in the Hall coefficient. µSR confirms long-range magnetic order up to 2.2 GPa, implying the emergence of a novel high-pressure magnetic phase. Moreover, X-ray diffraction data show no structural transition below 14 GPa, demonstrating that the magnetic and transport anomalies arise from intrinsic changes in the magnetic ground state rather than structural distortions. These findings reveal how pressure suppresses the triple-Q noncoplanar order and stabilizes a distinct high-pressure magnetic phase in Co_1/3TaS₂.

[1] P. Park et al., npj Quantum Mater. 7, 1 (2022).

[2] H. Takagi et al., Nat. Phys. 19, 961 (2023).

[3] P. Park et al., Nat. Commun. 14, 8346 (2023).