First-principles investigation of transition-metal doped Al₂B₂ and AlB₄ monolayers for spintronics

Two-dimensional spintronics has garnered significant attention in recent years, driven by the rapidly increasing demand for greater computational power from machine learning and AI workloads. This research investigates whether substitutional doping with the transition metals Mn, Fe, and Cr induces magnetism in two recently discovered, lightweight, two-dimensional Dirac nodal line semimetal monolayers, Al₂B₂ and AlB₄. Computations performed with density functional theory (DFT) reveal ferromagnetic ground states in nine of the twelve investigated monolayers. Defect formation energy calculations show that substitution on Al sites in both monolayers is thermodynamically preferred over B sites. The opening of gaps at band crossings is observed in band structures across all monolayers when spin-orbit coupling effects are introduced, suggesting nontrivial topologies of the pure materials are most likely retained. These findings identify doped Al₂B₂ and AlB₄ monolayers as promising platforms for the future exploration of two-dimensional spintronics.