Role of crystal and magnetic structures in the magnetoelectric coupling in ${\mathrm{CaMn}}_7{O}_{12}$

We investigate the magnetoelectric coupling in ${\mathrm{CaMn}}_7{O}_{12}$ (CMO) through a comprehensive spectroscopic analysis combining inelastic neutron scattering (INS), x-ray absorption spectroscopy (XAS), and synchrotron-based powder x-ray diffraction (PXRD). CMO's intricate interplay between magnetism and ferroelectricity is dissected to uncover its underlying mechanisms. XAS reveals a mixed valency of Mn ions in CMO, reflecting the presence of ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ ions, which contributes to its magnetoelectric properties. The double structure in Mn-$K$ near-edge absorption spectra reinforces multiple Mn sites as well as the mixed valency of the compound. Synchrotron-based PXRD experiments conducted over a range of temperatures unveil structural distortions near the magnetic transition temperatures of CMO. These distortions coincide with anomalies in lattice parameters and bond lengths, shedding light on the link between structural modulations and magnetoelectric behavior. Furthermore, INS measurements identify specific energy bands ($E_1$, $E_2$, and $E_3$) associated with distinct exchange interactions between Mn ions. This work advances our understanding of magnetoelectric coupling mechanisms and showcases the potential of multifunctional materials for applications in spintronics and related fields.