Computational Screening of 2D Pentagonal Materials with Room-Temperature Altermagnetism, Multiferroicity, and Topological States

• • High-throughput screening of 1470 binary configurations identified 37 dynamically stable pentagonal monolayers, including 24 previously unreported structures, expanding the design space for 2D materials. • • Room-temperature magnetism is achieved with ferromagnetic Curie temperature up to 521 K, antiferromagnetic Néel temperature up to 761 K, and altermagnetic Néel temperature of 984 K, enabling spintronic devices operating at ambient conditions. • • Altermagnetic semiconductor Mn4N2 exhibits giant spin splitting of 0.78 eV and pure spin-polarized transport window from −0.04 to 0.36 eV, with strain-tunable valley splitting of 18.2 meV under 4% uniaxial strain, offering tunable spin-valley coupling for quantum information processing. • • Type-II multiferroicity in Fe4C2 and Mn4C2 shows in-plane electric polarization of 1.408 and 1.564 pC/m, ferroelastic strain of 0.8% and 1.2%, and reversal chirality, enabling multifunctional devices with coupled ferroic orders.