Janus tetragonal Mn2BN monolayer: A 2D polar half-metal with coexistent ferroelectricity and magnetism

The integration of ferroelectricity, ferromagnetism, and half-metallicity in two-dimensional (2D) materials is pivotal for advancing spintronic device technologies. However, the progress in identifying such materials is limited, and we here propose a compelling approach by constructing asymmetry structures (Janus) based on known 2D magnets, namely, the Janus tetragonal Mn2BN monolayer as a promising polar half-metal. The asymmetric arrangement of B and N atoms, coupled with comparable atomic sizes and evident electronegativity, ensures structural stability and inherent polarization, while the dominance of Mn atoms governs magnetism. The robust ferromagnetic order stems from a strong super-exchange interaction, evident in the significant hybridization between Mn d and B/N p orbitals. The Mn2BN monolayer exhibits a wide spin bandgap (1.09 eV), a substantial electric polarization (9.15 μC cm−2), and a sizable magnetic anisotropic energy (238 μeV/Mn) and maintains stable ferromagnetic order to ∼800 K. These properties position it as a promising candidate for next-generation multifunctional devices in spintronics.