Pentagonal 2D Altermagnets: Material Screening and Altermagnetic Tunneling Junction Device Application

Abstract Altermagnetism, the third magnetic phase beyond ferromagnetism and antiferromagnetism, holds great promise for spintronics but also faces challenges in materials discovery and mechanism exploration. Here, through high‐throughput screening of 170 pentagonal 2D materials, 4 altermagnetic semiconductors (MnS ₂ , CoS ₂ , MnC ₂ , and CoPSe) are identified with sizable spin splitting (109–172 meV). It is shown that MnS ₂ is the first‐of‐kind altermagnetic second‐order topological insulator (AMSOTI), as evidenced by a nontrivial real Chern number (ν _R = 1) and spin‐polarized corner state. Using ab inito quantum transport simulation, a MnS ₂ ‐based altermagnetic tunneling junction (AMTJ) is designed and a giant tunneling magnetoresistance (TMR) of 1.5 × 10 ⁵ % at the Fermi level, which surpasses MF ₂ (M = Co and Ni)‐based AMTJ by three orders of magnitude. In addition, by applying a twisting angle of 90° to the AMTJ without altering the order, a significant TMR of 1.2 × 10 ⁷ % as driven by the structural changes is observed. This work unveils pentagonal 2D materials as a compelling material platform for exploring the physics and device applications of altermagnets.