Discovery of a novel half metallic 2D Cr2Se3 monolayer with high Curie temperature from correlated antiferromagnetic 2D CrSe2

Robust two-dimensional magnets are essential for next-generation spintronics. Using first-principles calculations, we demonstrate that only the antiferromagnetic 1H- and 1T-CrSe2 exhibit stable magnon dispersions. The preferred stability of 1T phase originates from spin-ordering polarization of correlated Cr-d states among three low-lying crystal-field levels. These levels are localized with distinct orbital character in the 1T phase, but delocalized in the 1H phase. The full occupation of low-lying levels leads to antiferromagnetic exchange, yielding Néel temperatures of 310 K (1T) and 274 K (1H). By introducing 25% Se line defects in CrSe2 monolayer, we predict a novel monolayer Cr2Se3 in H and T phases (analogous to their parent 1H/1T-CrSe2). Both Cr2Se3 phases are stable and are half-metallic, with spin (↓) band gaps of 1.39 eV (H) and 2.28 eV (T). Cr2Se3/h-BN heterostructures preserve the electronic properties, indicating feasible growth on h-BN substrates. In both phases, the partial occupation of the low-lying crystal-field levels enhances ferromagnetic exchange through hopping between occupied and unoccupied orbitals. Remarkably, Curie temperatures based on the Heisenberg Hamiltonian reach 547 K (H) and 606 K (T). The H phase satisfies the Stoner criterion, while the Heisenberg-like T phase shifts toward the Stoner regime under 2–4% biaxial tensile strain. These results position Cr2Se3 as a promising half-metallic 2D magnet.