The chiral magnetoelectric compound ${\mathrm{Ni}}_3{\mathrm{TeO}}_6$ is investigated through temperature-dependent synchrotron-based powder x-ray diffraction and x-ray absorption spectroscopy between 15 and 300 K. Our work provides direct evidence for the exchange-striction in the material around the concomitant onset point of collinear antiferromagnetic and the magnetoelectric phases. The x-ray absorption near edge spectra and x-ray photoelectron spectra show that the sample consists of both ${\mathrm{Ni}}^{2+}$ and ${\mathrm{Ni}}^{3+}$ ions in the lattice. The ionic state of Ni is found to be quite robust, and it is largely independent of the preparation route. Additionally, a minority ${\mathrm{Te}}^{4+}$ state is found to coexist with the majority ${\mathrm{Te}}^{6+}$ state, which may arise from the charge disproportionation between Ni and Te ions (${\mathrm{Ni}}^{2+} + {\mathrm{Te}}^{6+}\iff {\mathrm{Ni}}^{3+} + {\mathrm{Te}}^{4+}$). The observed mixed valency of Ni is also confirmed by the total paramagnetic moment (${\mu }_{\text{eff}}$) per Ni atom in the system. This mixed valency in the metal ions and the exchange-striction may be attributed to the observed magnetoelectric effect in the system.

• Received 7 September 2022
• Revised 8 December 2022
• Accepted 9 December 2022

DOI:https://doi.org/10.1103/PhysRevB.106.214437