Comparative Raman Scattering Study of Crystal Field Excitations in Co-based Quantum Magnets

Co-based materials have recently been explored due to potential to realise complex bond-dependent anisotropic magnetism. Prominent examples include Na_2Co_2TeO_6, BaCo_2(AsO_4)_2, Na_2BaCo(PO_4)_2, and CoX_2 (X = Cl, Br, 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_ 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.