Fig. 1: Conical helimagnetism in the layered square-lattice antiferromagnet DyTe₃.

a Crystallographic unit cell with covalently bonded DyTe bilayers and metallic Te bilayers. b Magnetic exchange interactions in a single DyTe double-square net bilayer. c Zigzag chain illustration of double-square net structure in DyTe₃. The interactions J₁, J₂ connect nearest and next-nearest neighbors in the zigzag chain model, respectively; but the inter-atomic distance is shorter for J₂, and its antiferromagnetic coupling strength is dominant. Conical, noncoplanar helimagnetism is resolved in the zero-field ground state by neutron scattering. The cone direction, parallel to the a-axis, alternates both between pairs of magnetic sites in a zigzag chain, and between stacked zigzag chains. This texture causes polarization along the b-axis, i.e., perpendicular to the square net bilayers (yellow arrow). The full magnetic unit cell extends two times further along the chain direction (Supplementary Fig. 1). d Weak anisotropy of the magnetic susceptibility χ in DyTe₃. The softest direction is H∥c, consistent with the modulation direction of the magnetic order in (c). The inset shows Curie–Weiss temperatures and temperatures T_χ of maximal χ, measured in a small magnetic field along three crystallographic directions. Error bars correspond to statistical uncertainties of Curie–Weiss fitting and temperature sampling width, respectively.