Bulk properties of Ni-intercalated metallic triangular antiferromagnet Ni_1/3NbS₂ and Ni_1/3TaS₂

TM_1/3MS₂ (TM = 3d transition metal, M = Nb, Ta) has recently been gaining increasing attention due to its wide variety of fascinating magnetic structures and the chiral arrangement of intercalated TM atoms. Here, we report the bulk properties of Ni_1/3NbS₂ and Ni_1/3TaS₂ by magnetization, transport, heat capacity, powder neutron diffraction, and X-ray absorption spectroscopy, which has received little attention compared to other TM_1/3MS₂. In particular, our work has determined the magnetic structure of Ni_1/3NbS₂ and Ni_1/3TaS₂ by neutron diffraction. Ni_1/3NbS₂ undergoes a phase transition at 84 K and develops antiferromagnetic helical order with a very long period along the c-axis (33c). On the other hand, a simple A-type spin configuration was observed for Ni_1/3TaS₂ below 158 K, where the spins are aligned to the c-axis. These magnetic structures, combined with lattice chirality and metallicity, can lead to various intriguing transport properties, making Ni_1/3TaS₂ and Ni_1/3NbS₂ promising material candidates for future studies on antiferromagnetic spintronics.