High-energy magnetodielectric effect in kagome staircase materials

Abstract

We use a combination of optical spectroscopy, first-principles calculations, and energy-dependent magneto-optical measurements to investigate the high-energy magnetodielectric effect in the frustrated kagome staircase compound ${\mathrm{Co}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ and develop structure-property relations in this family of materials. The optical spectra show two distinct Co on-site $d$ to $d$ excitations that can be assigned as deriving from spine and cross-tie sites, respectively. The energy separation between these features is substantially larger in ${\mathrm{Co}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ than in quasi-isostructural ${\mathrm{Ni}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$, indicating that the spine and cross-tie crystal field environments are more dissimilar in the Co compound compared with those in the Ni analog. Despite the similar appearance of the spectra, orbital correlation effects seem to dominate the optical properties of ${\mathrm{Co}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$, different from ${\mathrm{Ni}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$. Through the $6.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ ferromagnetic transition temperature, ${\mathrm{Co}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ displays $\ensuremath{\sim}2%$ dielectric contrast near $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, larger than that observed in the static dielectric constant. ${\mathrm{Co}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ also shows a high-energy magnetodielectric contrast of $\ensuremath{\sim}2%$ near $1.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ at $30\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, smaller than that of ${\mathrm{Ni}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ ($\ensuremath{\sim}16%$ near $1.3\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ at $30\phantom{\rule{0.3em}{0ex}}\mathrm{T}$). We attribute this result to the lack of strong lattice coupling at the low temperature magnetic phase boundaries.