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arXiv · 2507.09663

A Surface-confined Spiral State With the Double Period in the Cubic Chiral Helimagnet Cu$_2$OSeO$_3$

Priya R. Baral·Oleg I. Utesov·Samuel H. Moody·Matthew T. Littlehales·Pierluigi Gargiani·Manuel Valvidares·Robert Cubitt·Nina-Juliane Steinke·Chen Luo·Florin Radu·Arnaud Magrez·Jonathan S. White·Victor Ukleev
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Abstract

The chiral magnetoelectric insulator Cu$_2$OSeO$_3$ 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 Cu$_2$OSeO$_3$. This surface-confined spiral state (SSS) displays a real-space pitch of $\sim$120 nm, which remarkably is twice the length of the incommensurate structures observed to-date in Cu$_2$OSeO$_3$. The SSS phase emerges at temperatures below 30~K when the magnetic field is applied between $3^\circ$ to $18^\circ$ away from the $\langle\text{110}\rangle$ 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.

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Priya R. Baral, Oleg I. Utesov, Samuel H. Moody, Matthew T. Littlehales, Pierluigi Gargiani, Manuel Valvidares, Robert Cubitt, Nina-Juliane Steinke, Chen Luo, Florin Radu, Arnaud Magrez, Jonathan S. White, Victor Ukleev. 2025-07-13. A Surface-confined Spiral State With the Double Period in the Cubic Chiral Helimagnet Cu$_2$OSeO$_3$. https://arxiv.org/abs/2507.09663

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