Electronic and structural aspects of the chiral helimagnetic compound Cu[formula omitted]OSeO[formula omitted].

The electronic state and the structural properties of the helical magneto-electric material Cu 2 OSeO 3 is investigated through temperature-dependent synchrotron based x-ray diffraction and x-ray absorption spectroscopy. The x-ray absorption spectra on Cu and Se- K edges indicate that Cu and Se ions are in the 2＋ and 4＋ charge states respectively. The pre-edge corresponding to K -line of Cu in the x-ray absorption spectra cannot be fitted using a single Lorentzian function. At least two different Lorentzian lines are required to fit the pre-edge, which are separated by ∼ 0. 6 ± 0. 042 eV. This separation originates due to the difference in the crystallographic environment of Cu(1) and Cu(2) and the subsequent difference in the energy of the 3 d orbitals of two Cu sites. The obtained energy difference reconfirms the value reported using resonant inelastic x-ray scattering and maximally localized Wannier function calculation. The synchrotron based powder x-ray diffraction indicates significant anomaly in the Cu-O-Cu bond angle around the magnetic transition temperature ( T C ∼ 59 K). Interestingly, the sample show negative thermal expansion in the lattice parameter below T C. Such anomalies can be connected to the exchange-striction mechanism. • Anomalous structural variation in a helical magneto-electric material Cu 2 OSeO 3. • Presence of exchange striction at the magnetic transition. • X-ray absorption spectroscopy indicates ＋2 and ＋4 ionic states of Cu and Se, respectively. • Multiple peak structure of the pre edge of x-ray absorption spectroscopy data corroborating two inequivalent positions of Cu. [ABSTRACT FROM AUTHOR]