“…While the focus has largely been on the main-group-element-based compositions due to their high performance in optoelectronic devices, 1,2 the relative dearth of transition-metal-based halide perovskites offers a tantalizing opportunity to explore new compositions with magnetic cations. 3 Furthermore, drawing structure−property relationships in magnetic metal halides will facilitate a deeper understanding of the interactions between composition, geometry, and magnetism in metal halides, paving the way toward their use in, for example, spintronics 4 and data storage. 5 The vacancy-ordered halide double perovskites (VDPs), having the general formula A 2 I B IV X 6 where A is a monovalent cation, B is tetravalent metal, and X is a halide, can accommodate a wide swath of the periodic table into their B-site, including several magnetic B-site cations.…”