Effects of Jahn-Teller distortion on the skyrmion stability of (Cu_1-xNi_x)₂OSeO₃

We explore the Jahn-Teller distortion of Ni²⁺ ions on the skyrmion phase of Cu₂OSeO₃. Polycrystalline (Cu_1-xNi_x)₂OSeO₃ (0 ≤ x ≤ 0.06) samples were synthesized by solid-state reaction. X-ray diffraction, X-ray absorption near-edge spectroscopy, extended X-ray absorption fine structure spectroscopy, magnetic and magnetodielectric measurements were performed and comprehensively analyzed. These revealed that the Ni²⁺ ion occupies both the Cu sites almost equally, and the Jahn-Teller distortion of the Ni²⁺ ion invokes a change in the local trigonal bipyramidal structure, which has a significant influence on the H-T magnetic phase diagram and electrical polarization of (Cu_1-xNi_x)₂OSeO₃. A large enhancement of the skyrmion area upon Ni-doping can be ascribed to the magnetic anisotropy of the Jahn-Teller active Ni²⁺ ion in the Cu(i) site. The observed results indicate that chemical doping is a unique way to control and manipulate skyrmion boundaries in Cu₂OSeO₃.