Comparative Raman scattering study of crystal field excitations in Co-based quantum magnets

Co-based materials have recently been explored because of their potential to realize complex bond-dependent anisotropic magnetism. Prominent examples include ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6, {\mathrm{BaCo}}_2{\left({\mathrm{AsO}}_4\right)}_2, {\mathrm{Na}}_2\mathrm{BaCo}{\left({\mathrm{PO}}_4\right)}_2$, and ${\mathrm{Co}\mathit{X}}_2$ $(X=\mathrm{Cl},\mathrm{Br},\mathrm{I})$. In order to provide insight into the magnetic interactions in these compounds, we make a comparative analysis of their local crystal electric field excitations spectra via Raman scattering measurements. Combining these measurements with theoretical analysis confirms the validity of $j_{\mathrm{eff}}=1/2$ single-ion ground states for all compounds, and provides accurate experimental estimates of the local crystal distortions, which play a prominent role in the magnetic couplings between spin-orbital coupled Co moments.