Effect of interfaces on band hybridization, orbital polarization, and helical magnetism in SrFeO₃/CaFeO₃ heterostructures

The alkaline earth ferrates exhibit an array of interesting physical phenomena such as metal-insulator transitions, strong Fe-O covalency, rapid redox reactions, and helical magnetism. In this talk, I will present how the Fe-O band hybridization and Fe 3d orbital occupancy changes across interfaces in isoelectronic SrFeO₃/CaFeO₃ superlattices. A consequence of the strong hybridization in these materials is that their electronic configuration can be described as containing both d⁴L⁰ and d⁵L¹ contributions, where L indicates a ligand hole. Using resonant soft x-ray reflectivity, we find a modulation of the Fe-O hybridization across the superlattice with SrFeO₃ hosting a larger ligand hole density than CaFeO₃.[1] We show that the Fe e_g orbital polarization is correlated with the degree of d⁴L⁰ electronic character present in the layers. Results will also be presented on the stability of the helical magnetic order in (CaFeO₃)₂₀/(SrFeO₃)_n superlattices. Using resonant x-ray diffraction, we show that the helical magnetic order coherently propagates through superlattices with n = 1 but does not extend through the SrFeO₃ layer in a superlattice with n = 6.[2] We describe these results in context of recently reported multi-q helimagnetism in SrFeO₃, while our results support single-q helimagnetism in CaFeO₃.
[1] P. C. Rogge, P. Shafer, G. Fabbris, W. Hu, E. Arenholz, E. Karapetrova, M. P. M. Dean, R. J. Green, S. J. May, Advanced Materials 31, 1902364 (2019).
[2] P. C. Rogge, R. J. Green, R. Sutarto, and S. J. May, Physical Review Materials 3, 084404 (2019).