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  Baral, P. R.; Utesov, O. I.; Moody, S. H.; Littlehales, M. T.; Gargiani, P.; Valvidares, M.; Cubitt, R.; Steinke, N.-J.; Luo, C.; Radu, F.; Magrez, A.; White, J. S.; Ukleev, V.: A surface-confined spiral state with the double period in the cubic chiral helimagnet Cu₂OSeO₃. npj Quantum Materials early view (2026)

10.1038/s41535-026-00892-6
Open Access Version

Abstract:
The chiral magnetoelectric insulator Cu2OSeO3 hosts a rich and anisotropic magnetic phase diagram that includes helical, conical, field-polarised, tilted conical, and skyrmion lattice phases. Using resonant elastic x-ray scattering (REXS), we uncover a new spiral state confined to the surface of Cu2OSeO3. This surface-confined spiral state (SSS) displays a real-space pitch of ~ 120 nm, which remarkably is twice the length of the incommensurate structures observed to-date in Cu2OSeO3. The SSS phase emerges at temperatures below 30 K when the magnetic field is applied between 3? to 18? away from the ?110? crystallographic axes. Its surface localisation is demonstrated through a combination of REXS in reflection and transmission geometries, with complementary small-angle neutron scattering measurements suggesting its absence from the bulk. We attribute the stabilisation of the SSS to competing anisotropic interactions at the crystal surface. The discovery of a robust, surface-confined spiral paves the way for engineering energy-efficient, nanoscale spin-texture platforms for next-generation devices.