Abstract
Spontaneous Hall conductivity has recently been reported in the triangular lattice antiferromagnet Co1/3TaS2 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 Co1/3TaS2 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≤x≤0.325, CoxTaS2 keeps all the characteristics of the ground state consistent with the previous studies—two antiferromagnetic phase transitions at TN1 and TN2 (<TN1), a large spontaneous Hall conductivity [σxy(H=0)], and a weak ferromagnetic moment along the c axis. However, samples with x≥0.330 exhibit distinct bulk properties, including the absence of both σxy(H=0) and the weak ferromagnetic moment. Our neutron diffraction data reveal that CoxTaS2 with x≥0.330 develops coplanar helical magnetic order with qm1=(1/3, 0, 0). This is entirely different from what has been seen in x≤0.325, explaining the observed composition dependence.
