Alloying two-dimensional NbSi₂N₄: a new strategy to realize half-metallic antiferromagnets

Finding two-dimensional (2D) materials with both 100% spin polarization and zero net magnetic moment is essential for next-generation spintronics. Half-metallic antiferromagnets (HMAFs) are ideal materials to satisfy these exigent needs, but such a system has never been found among 2D inorganic materials. In this paper, we theoretically demonstrate that intrinsic 2D HMAFs can be realized by alloying Nb with Mn in 2D septuple-atomic-layer NbSi₂N₄. By continuously incorporating Mn, the stronger Mn-N hybridization relative to Nb-N induces a metal to half-metal to semiconductor transition. The competitive coupling between the Nb-d itinerant electron spin and the Nb-Mn d-d direct interaction drives the ferromagnetic to antiferromagnetic phase transition. For the first time in 2D inorganic materials, the exact cancellation of local magnetic moments and band gap opening in one spin channel is obtained simultaneously at a Nb/Mn ratio of 3 : 1, as demonstrated by our first-principles calculations. The present results would not only inspire materials design of more 2D HMAFs in the future but also impel the advancement of next-generation antiferromagnetic spintronic devices.