Prediction of room-temperature half-metallicity in layered halide double perovskites

Half-metallic ferromagnets (HMFs) that possess intriguing physical properties with completely spin-polarized current are key candidates for high-efficiency spintronic devices. However, HMFs that could simultaneously have high Curie temperature (T_c), wide half-metallic gap (Δ_HM), and large bulk magnetocrystalline anisotropy energy (MAE) are very rare, which significantly restrict their room-temperature (RT) applications. In this article, through materials screening in layered halide double perovskites (LHDPs), we have theoretically identified that Cs₄FePb₂Cl₁₂, which has good crystallographic, dynamic and thermal stabilities, possesses an intrinsic half-metallic ground-state with a high T_c ~ 450 K. Interestingly, the long-range ferromagnetic ordering in bulk Cs₄FePb₂Cl₁₂ is contributed by the strong super-superexchange interactions between the neighboring Fe d orbitals mediated by different anionic Cl p orbitals. The high T_c of layered Cs₄FePb₂Cl₁₂ can be well maintained even in the monolayer limitation, i.e., T_c ~ 370 K for Cs₄FePb₂Cl₁₂ monolayer, which is critical for nanoscale device applications. Moreover, both bulk and monolayer Cs₄FePb₂Cl₁₂ can exhibit wide Δ_HM ~ 0.55 eV and large MAE >320 μeV/Fe, comparable to that of the best HMFs reported in the literature. Our findings can significantly extend the potentials of LHDPs for high-temperature spintronic applications.