Fully spin-polarized nodal-chain half-metal in transition metal nitrides

Abstract

Half-metals, owing to their 100% spin polarization, have attracted considerable attention in recent years due to their significant potential for spintronic applications. Here, based on first-principles calculations and theoretical analysis, we reveal that the transition metal nitrides XN4 (X = Mn, Fe, Co) represent a novel class of fully spin-polarized nodal-chain half-metals, uniquely integrating the key characteristics of conventional half-metals and topological nodal-chain semimetals. These compounds are predicted to stabilize in a ferromagnetic ground state. We demonstrate that, in the absence of spin–orbit coupling (SOC), the electronic structure near the Fermi level is dominated exclusively by a single spin channel, thereby achieving 100% spin polarization. Furthermore, several spin-polarized energy bands near the Fermi level are entangled, with their crossing points forming a complex nodal-chain structure within the Brillouin zone. We show that this spin-polarized nodal chain also gives rise to spin-polarized surface states. When SOC is included, we find that these materials exhibit very small magnetic anisotropy, implying that the magnetization can be more easily controlled. We further show that while SOC has little effect on the bulk band structure, it induces a sizable anomalous Hall conductivity. Our results suggest that the XN4 (X = Mn, Fe, Co) compounds are promising material platforms for topological spintronic devices.