Room-Temperature Altermagnetic Nb ₂ OX ₂ (X = S, Se, Te) Monolayers with Controllable Valley Polarization: Implications to Spintronic Devices

Altermagnets, which combine the advantages of ferromagnets and antiferromagnets, provide opportunities for advancing spintronics or valleytronics. Here, we propose a type of room-temperature altermagnet, Nb 2 OX 2 (X = S, Se, Te) monolayers, based on first-principles calculations. The Nb 2 OX 2 monolayers have spin-layer coupling by locking spin and valleys to the NbX indices, resulting in layer-locked spin-polarized band edges. Both Nb 2 OS 2 and Nb 2 OSe 2 monolayers exhibit perpendicular magnetic anisotropy, while the Nb 2 OTe 2 monolayer has in-plane magnetization anisotropy. Under uniaxial strains and a vertical electric field, the Nb 2 OX 2 monolayers exhibit significant valley polarization, achieving the coordinated regulation of valley and spin. Our results pave the way for altermagnet applications in nanoscale spintronic devices.