Symmetry-engineered 2D Janus Fe2BN as a <i>d</i> -wave altermagnet with ferroelectricity and anomalous Hall effect

Altermagnets, characterized by compensated magnetic moments and spin-split electronic bands, provide a promising platform for next-generation spintronics. However, two-dimensional (2D) altermagnets that intrinsically combine magnetism, ferroelectricity, and transport tunability remain extremely scarce. Here, we propose a Janus Fe2BN monolayer as a 2D d-wave altermagnet that intrinsically integrates antiferromagnetism, ferroelectricity, and strain-tunable anomalous transport. Strong Fe–Fe direct exchange stabilizes a robust checkerboard Néel order with a high Néel temperature of 291 K. The intrinsic B–N asymmetry generates a switchable out-of-plane ferroelectric polarization with a low energy barrier (0.80 eV/f.u.), whose reversal couples to magnetism and transiently drives a spin-polarized ferromagnetic state. Moreover, uniaxial strain lifts valley degeneracy by tuning electronic symmetry, activating a sizable anomalous Hall conductivity, and enhancing the spin Hall conductivity. These results establish Fe2BN as a symmetry-engineered 2D platform for electrically and mechanically tunable spintronic functionalities rooted in altermagnetism.