Cu₂OSeO₃ turns trigonal with structural transformation and implications for skyrmions

The formation and characteristics of magnetic skyrmions are strongly governed by the symmetry of the underlying crystal structure. In this study, we report the discovery of a new trigonal polymorph of Cu₂OSeO₃, observed exclusively in nanoparticles. Electron diffraction and density functional theory calculations confirm its R3m space group, sharing C_3v symmetry with Néel-type skyrmion hosts. This polymorph is likely stabilized by surface effects, suggesting that size-induced structural changes may drive a transformation from Bloch-type to Néel-type skyrmions in Cu₂OSeO₃. This hypothesis could be consistent with prior unexplained observations of Néel-type skyrmions at the surfaces of bulk crystals, which may result from surface-specific structural distortions. Overall, these findings provide insights into the interplay between size, structure, and magnetism, opening pathways for controlling skyrmionic properties in nanoscale systems.