Electronic structure of spin-orbit coupled vacancy ordered transition metal halides and formation of large magnetic...

Vacancy-ordered antifluorite materials (A₂BX₆) are garnering renewed attention as novel magnetic states driven by spin-orbit coupling (SOC) can be realized in them. In this work, by pursuing density functional theory calculations and model studies, we analyze the ground state electronic and magnetic structure of face-centered cubic antifluorites K₂ReCl₆(KReC, 5d³), K₂OsCl₆(KOsC, 5d⁴), and K₂IrCl₆(KIrC, 5d⁵). We find that KReC stabilizes in the high-spinS = 3/2 state due to large exchange-splitting as compared to the SOC strength. The KOsC stabilizes inS = 1 simple Mott insulating state while KIrC stabilizes inJeff = 1/2 spin-orbit-assisted Mott insulating state. The presence of an isolated metal-chloride octahedron makes these antifluorites weakly coupled magnetic systems with the nearest and next-nearest-neighbor spin-exchange parameters (J₁andJ₂) are of the order of 1 meV. For KReC and KOsC, theJ₁andJ₂are estimated to be antiferromagnetic and ferromagnetic, which leads to a Type-I antiferromagnetic ground state, whereas for KIrC, bothJ₁andJ₂are antiferromagnetic, hence, it stabilizes with a Type-III antiferromagnetic state. Interestingly, in their equilibrium structure, these antifluorites possess large magnetic anisotropy energy (MAE) (0.6-4 meV/transition metal), which is at least one-to-two orders higher than traditional MAE materials like transition metals and multilayers formed out of them. Moreover, with epitaxial tensile/compressive strain, the MAE enhances by one order, becoming giant for KOsC (20-40 meV/Os).