EPFL–PSI–HZB–ALBA collaboration discovers surface-confined spiral state in Cu2OSeO3; surface spiral period doubles bulk helix
Surface-confined spiral state with a doubled magnetic period in Cu2OSeO3
Head of PSI Center for Neutron and Muon Sciences
Surface-confined spiral state with a doubled magnetic period in Cu2OSeO3
Magnetism in solid materials originates from tiny atomic “compasses” called electron spins. In many magnetically ordered compounds, these spins simply align parallel or antiparallel to each other. However, in more complex systems they can arrange into intricate patterns in space, forming spin textures, where the direction of magnetization continuously rotates from point to point. Such textures include spirals and topological vortex-like structures (skyrmions), and are currently of great interest because they could be used to store and process information in future energy-efficient technologies.
One important class of materials hosting such states are chiral magnets, where the lack of inversion symmetry leads to a twisting interaction between neighboring spins. In the prototypical cubic chiral compound Cu2OSeO3, this interaction stabilizes a helical spin structure with a well-defined spatial period of 60 nanometers determined by the balance of competing magnetic forces.
In a recent study, an international collaboration including École Polytechnique Fédérale de Lausanne, Paul Scherrer Institute (Switzerland), Helmholtz-Zentrum Berlin (Germany) and the ALBA Synchrotron (Spain) has discovered a previously unknown magnetic state localized near the surface of Cu2OSeO3. Using resonant elastic x-ray scattering (REXS) at ALBA, the team discovered a spiral modulation whose period is twice that of the bulk helix. Complementary small-angle neutron scattering (SANS) experiments performed at SANS-I (PSI) and D33 (ILL) confirmed its absence from the bulk part of the crystal — a surprising result that reveals how magnetic interactions at the surface can differ markedly from those inside the material.
These results demonstrate that surfaces can host distinct magnetic states, opening new opportunities to tailor spin textures by engineering interfaces and thin films. Beyond fundamental interest, controlling such surface-confined magnetic structures could provide new ways to design functional materials for next-generation spintronic devices, where information is encoded in nanoscale magnetic patterns rather than electric charge.
Reference:P.R. Baral et al, npj Quantum Materials (2026) - adv. online publication
PSI Center for Neutron and Muon Sciences