Chemical design of monolayer altermagnets

The crystal-symmetry-paired spin-momentum locking (CSML), arising from the intrinsic crystal symmetry that connects different magnetic sublattices in altermagnets, enables many exotic spintronics properties, such as unconventional piezomagnetism and non-collinear spin currents. However, the shortage of monolayer altermagnets restricts further exploration of dimensionally confined phenomena and applications of nanostructured devices. Here, we propose general chemical design principles inspired by sublattice symmetry of the layered altermagnet V[Formula: see text](Se,Te)[Formula: see text]O through symmetry-preserving structural modification and valence-adaptive chemical substitutions. In total, we construct 2600 candidates across four structural frameworks, M[Formula: see text]A[Formula: see text]B[Formula: see text] and their Janus derivatives. High-throughput calculations identify 612 potential altermagnets with Néel-ordered ground states, among which 79 exhibit CSML Dirac cones that enable spin-polarized ultra-fast transport. These materials also feature different ground-state magnetic orderings and demonstrate diverse electronic behaviors, ranging from semiconductors and metals to half-metals and Dirac semimetals. This work not only reveals abundant monolayer altermagnets, but also establishes a rational principle for their design, opening the gates to the exploration of confined magnetism and spintronics in atomically thin systems.