Many studies of non-relativistic spin-splitting (NRSS), or altermagnetism, have focused on idealized, perfectly ordered crystals, relying on symmetry-based approaches to identify candidate materials. Here, we theoretically investigate how local short-range ordering (SRO) influences NRSS of energy bands in partially ordered collinear antiferromagnetic iron oxyfluoride (FeOF). Using the cluster expansion method, we identify four nearly degenerate structures (energy difference ≤8 meV per formula unit) that represent distinct snapshots of local plane-to-plane O/F correlations. Our density functional theory (DFT) results show robust NRSS along the Γ-M direction in all four structures, despite the absence of long-range order. The magnitude and character of the splitting depend sensitively on the specific direction of anion correlations, effects that are not fully captured in high-symmetry average structures. Notably, two configurations (Pmc21 and Pm) exhibit Γ-point spin splitting absent in ordered FeF2 and a virtual crystal approximation model of FeOF. We further predict distinct magneto-optical Kerr effect (MOKE) signatures, enabling experimental detection of SRO-driven electronic structure changes. These results highlight heteroanionic compounds as a promising design space for NRSS antiferromagnets, with experimentally synthesized FeOF already exhibiting a substantially higher N\'eel temperature (315\,K) than FeF2 (79\,K).
@article{arxiv.2512.12179,
title = {Anion correlation induced nonrelativistic spin splitting in rutile antiferromagnets},
author = {Siddhartha S. Nathan and Danilo Puggioni and Linding Yuan and James M. Rondinelli},
journal= {arXiv preprint arXiv:2512.12179},
year = {2025}
}