Geometry-induced spin chirality in a non-chiral ferromagnet at zero field

Spin chirality is a fundamental property that manifests non-reciprocal transport-magnetochiral anisotropy (MChA). However, the application of MChA in technology is constrained by the necessity for an external magnetic field, complex non-centrosymmetric crystal synthesis and cryogenic environments. Here we overcome these challenges by imprinting geometric chirality onto a nickel tube via three-dimensional nanoengineering. We use two-photon lithography to create a structurally twisted polymeric template with micrometre-sized pitch and diameters and cover it with a uniform 30-nm-thick nickel shell. The nickel tube exhibits spontaneous MChA-non-reciprocal transport at zero magnetic field and room temperature. X-ray magnetic circular dichroism microscopy confirms helical spin textures stabilized by the torsion- and curvature-engineered shape anisotropy, while inelastic light scattering spectroscopy demonstrates robust non-reciprocal magnon transport at remanence, reconfigurable via magnetic field history. The chiral parameter in our device surpasses that of natural chiral magnets such as Cu₂OSeO₃. Analytical theory and micromagnetic simulations demonstrate that the non-reciprocity is further enhanced by downscaling the feature sizes. Our results establish a scalable, geometry-driven nanotechnology that imprints spin chirality on non-chiral ferromagnets and may enable nanoscale integration of chirality-enhanced magnonics and spintronics for real-world use cases.