Abstract
<jats:p>Transition metal halide perovskites (TMHPs) offer tunable magnetic properties through compositional flexibility, but systematic understanding of how transition metal (TM) identity and halide chemistry govern magnetic exchange remains limited. In this work, we present a comprehensive computational investigation of magnetic interactions across 40 TMHPs (CsMX3, M = Sc-Zn, X = F, Cl, Br, I) using density functional theory with Hubbard U corrections (DFT+U) and tight-binding exchange parameter extraction (TB2J). Three distinct classes of magnetic behavior emerge. First, the majority of TMHPs (M = V, Mn, Fe, Co, Ni) exhibit antiferromagnetic (AFM) ordering consistent with superexchange interactions described by Goodenough-Kanamori (GK) rules. Second, Ti and Cr systems exhibit ferromagnetic (FM) ordering, with Ti compounds showing metallic electronic structures consistent with Stoner-type itinerant ferromagnetism, while Cr compounds display behavior indicative of orbital-ordered superexchange. Third, Sc and Cu systems exhibit halide-dependent magnetism governed by the redox instability of their divalent states, while Zn systems are non-magnetic due to their diamagnetic electron configuration. Across the halide series, chloride compounds consistently exhibit the strongest exchange interactions, followed by bromides, reflecting an optimal balance between bond length and covalency that maximizes superexchange hopping. Exchange strength in AFM systems increases systematically across the 3d series, with late TMs such as Ni exhibiting the strongest coupling due to enhanced metal-halide covalency. Additionally, anisotropic exchange interactions are observed primarily in systems with electron occupation in eg orbitals and are enhanced in heavier halides, suggesting an interplay between orbital character, lattice distortions, and possible spin-orbit effects. These results establish general chemical trends and design principles for magnetic TMHPs, including strategies to tune magnetic ordering, exchange strength, and magnetic dimensionality through targeted selection of TM and halide elements. This work provides a foundation for the rational design of magnetic halide perovskites and motivates further investigation into their structural and relativistic effects.</jats:p>