Comparative study of FeCr2S4 and FeSc2S4: Spinels with orbitally active A site

Using first-principles density-functional calculations, we perform a comparative study of two Fe-based spinel compounds, FeCr2S4 and FeSc2S4. Though both systems contain an orbitally active A site with an Fe2+ ion, their properties are rather dissimilar. Our study unravels the microscopic origin of their behavior driven by the differences in hybridization of Fe d states with Cr/Sc d states and S p states in the two cases. This leads to important differences in the nature of the magnetic exchanges as well as the nearest-versus next-nearest-neighbor exchange parameter ratios, resulting into significant frustration effects in FeSc2S4 which are absent in FeCr2S4.