Effect of short-range anion ordering on altermagnetism in rutile FeOF

Recent finding of non-relativistic spin splitting (NRSS) in antiferromagnets holds promise for spintronics applications. Most studies of NRSS to date have focused on idealized, perfectly ordered crystals, using symmetry-based approaches to identify candidate materials. Here, using density functional theory calculations and cluster expansion models, we investigate how short-range anion ordering influences the non-relativistic spin splitting in the Brillouin zone of a collinear antiferromagnet, using the rutile iron oxyfluoride FeOF as a representative heteroanionic material. We find robust NRSS along the Γ-M direction despite the lack of long-range order. We further show that the magnitude and nature of the splitting depend sensitively on the anion correlations, effects that are not fully captured in a high-symmetry average structure. Our results highlight the promise of heteroanionic compounds as a broader design space for NRSS antiferromagnets, with FeOF already offering a higher Neel temperature than FeF₂.