Probing the Magnetic Interactions in CaMn7O12: Insights into Large Magnetoelectric Coupling and Ferroelectric Polarization

The compound CaMn7O12 has recently attracted significant attention for its extraordinary magnetoelectric coupling and highest ferroelectric polarization among magnetic multiferroics reported so far. We employ a multi-modal approach using inelastic neutron scattering (INS), X-ray absorption spectroscopy, and temperature-dependent X-ray diffraction to probe the magnetic excitations and interactions in CaMn7O12. If we consider the modulated ferroaxial crystal structure, the exchange interactions are modulated along the c -c-direction. Utilizing the SpinW software package for theoretical modelling, we capture the complex, multi-site magnetic interactions and incommensurately modulated magnetic structure of the compound. The model successfully reproduces the experimental INS intensity and the Bose-corrected 2D color plots reveal three distinct energy bands corresponding to spin-wave dispersion modes. By systematically switching on and off various exchange interactions in the SpinW simulation, we identify key contributions to the observed large magnetoelectric coupling and ferroelectric polarization. This study provides valuable insights into the origins of these remarkable properties in CaMn7O12 and expands our understanding of magnetic interactions in complex multiferroic systems.