Broadening Hard‐Magnet Discovery Beyond Symmetry Constraints via Unified Effective Anisotropy

ABSTRACT Machine‐learning‐driven discovery of rare‐earth‐lean hard magnets has advanced rapidly, yet existing pipelines have remained constrained either to a fixed composition family or to a single crystal‐system class, leaving most compositional and structural space unexplored. We address both limitations by introducing a unified effective anisotropy constant, K eff , defined consistently across all seven crystal systems, equal to the conventional K 1 in uniaxial cases and—as established here by symmetry‐based derivation and density functional theory calculations—designed to approximate the minimum magnetization‐reversal barrier that governs the hardness parameter κ in orthorhombic, monoclinic, and triclinic systems, with symmetry‐dependent accuracy quantified by angular DFT sampling. With this descriptor, we assemble a magnetocrystalline‐anisotropy database and train a two‐stage classi…