Researchers from EPFL, Max Planck Institute and HZB have shown that spin chirality can be engineered purely by 3D shape in an otherwise non‑chiral ferromagnet, unlocking spontaneous MChA at room temperature and zero applied field.
The device is a hollow “Archimedean screw”: a 3D‑printed polymer tube made by two‑photon lithography and conformally coated with a ~30 nm polycrystalline Ni layer by ALD, forming a twisted nanotube whose left‑ or right‑handed geometry imprints the magnetic twist. The curved, twisted shape creates a helical magnetization pattern with a built‑in magnetic “circulation”, which breaks symmetry between +k and −k spin waves without needing exotic chiral crystals or external magnetic fields.
Magnetic imaging shows that the zero‑field spin texture follows the structural handedness and can be flipped by modest axial fields, giving two stable chiral states at remanence that encode the sign of this circulation. Micro‑BLS on thermally excited magnons then reveals strong non‑reciprocity in both frequency and intensity between counter‑propagating spin waves, with a sizeable asymmetry at zero field and a magnetochiral parameter on par with, or better than, classic chiral magnets—but here in simple Ni and at room temperature.
Modelling shows that this non‑reciprocity stems from the combination of the tube’s magnetic circulation and a geometry‑induced phase picked up by magnons, both controlled by the helix angle, tube radius and mode index m. In practice, the lowest mode supports directional information transport with a clear frequency shift, while higher modes can be tuned for diode‑like behavior and one‑way coupling—key ingredients for magnonic rectifiers and 3D spin‑wave links.
For spintronics, the message is that “material chirality” becomes a design choice of the 3D layout rather than a fixed property of the crystal: MChA, rectification and polarity‑dependent transport can be built into standard ferromagnets via geometry, and are expected to be even stronger in ALD‑compatible alloys such as permalloy. This points toward application‑specific, 3D‑printed chiral magnonics where non‑reciprocal spin‑wave transport is co‑designed with the device shape instead of the crystal structure.