Frustrated magnetic correlations in Cairo lattice material

Geometric frustration in magnetic materials can occur in structures based on polygons that contain an odd number of antiferromagnetically interacting atoms on the vertices. The Cairo lattice is one such structure built upon frustrated pentagons, which might induce interesting physics different from triangle-based lattices^[1]. Here, we report our recent diffuse neutron scattering study on a prototype Cairo pentagonal lattice material Bi₂Fe₄O₉^[2] with Ga substitution. Combining with computational simulation and advanced 3D-mΔpdf analysis, we show that there exist two types of short-range magnetic orders buried in a previously thought single spin glass state in Bi₂Fe_4-xGa_xO₉ with Ga substitution. These are distinct from the non-collinear magnetic order in the undoped compound Bi₂Fe₄O₉. Our results indicate a high tunability of magnetic correlations on the frustrated Cairo lattice. We compare the results from different simulations and analysis methods, and this comparison testifies to their suitability and robustness in solving short-range correlations in complex/disordered materials.