High-Energy Magneto-Dielectric Effect in Co$_{3}$V$_{2}$O$_{8}$.*

We investigate the optical and magneto-optical properties of the Kagom\'{e} staircase compound Co$_{3}$V$_{2}$O$_{8}$ in order to explore mechanistic aspects of the high-energy magneto-dielectric effect. Co$_{3}$V$_{2}$O$_{8}$ displays a much smaller dielectric contrast compared to quasi-isostructural Ni$_{3}$V$_{2}$O$_{8}$, a result that we attribute to a high-temperature local structural distortion in Co$_{3}$V$_{2}$O$_{8}$ along the cross-tie direction. Such a distortion prevents the low temperature magnetic transitions from having a strongly coupled lattice component. This proposition is supported by vibrational studies.