Tuning local magnetism of Penta-AlN₂via main-group metal adsorption

Using density functional theory, we systematically investigated the adsorption of four light main-group metal atoms (Li, Na, Mg, Al) on a (2 × 2) Penta-AlN₂ monolayer, focusing on their local magnetic regulation capabilities. All adatoms preferentially occupy N-N bridge sites, forming strong ionic adsorption with substantial charge transfer to the substrate. Crucially, this charge transfer is highly localized: it selectively quenches the magnetic moments of the two nearest-neighbor N atoms while leaving those of distant N atoms (approximately ±0.3µ_B) essentially unchanged. This atomically selective magnetic switching breaks the compensated antiferromagnetic order, thereby generating a net magnetic moment. Quantitative analysis of the exchange coupling reveals that the pristine monolayer exhibits strong antiferromagnetic coupling (-27 meV), which weakens to -1.25 meV upon Li adsorption and switches to ferromagnetic coupling (+0.5 to +2.5 meV) for Na, Mg, and Al, with the magnetic ground state transitioning from sAFM (Li) to FM (Na/Mg/Al). Crystal orbital Hamilton population (COHP) analysis reveals that the donated electrons weaken the proximal N-N bond and disrupt the antiferromagnetic exchange channel along it. Moreover, the switching efficiency can be tuned by choosing adatoms with different ionic radii, charge states, and electronic configurations. These findings demonstrate that MA adsorption provides a promising route toward atomically localized magnetic switching in two-dimensional semiconductors, with potential applications in ultrahigh-density data storage and spin-based logic devices, where individual atomic sites serve as independent functional units.