High-temperature nodal ring semimetal in two-dimensional honeycomb-kagome Mn ₂N ₃ lattice

The search for two-dimensional (2D) nodal ring semimetallic materials is a current research hotspot in spintronics, and designing a 2D nodal ring (NR) material with high Curie temperature ( T _C) and strong robustness to spin–orbit coupling (SOC) is an even greater challenge. Here, based on the first-principles calculations and symmetry analysis, we predict that 2D Mn ₂N ₃ is a nodal ring semimetal (NRSM) with three energy bands near the Fermi energy level consisting of electrons in the same spin channel. An electron-like energy band and two hole-like energy bands near the Fermi plane cross to form two NRs centered at the point Γ. Symmetry analysis shows that the spin-polarized NR semimetal is robust to SOC due to the conservation of horizontal mirror symmetry. Monte-Carlo simulations further demonstrate that the T _C of the 2D Mn ₂N ₃ reaches 530 K, well above the room temperature. Notably, the 2D Mn ₂N ₃ remains an NRSM on h-BN substrate. Our results not only reveal a general framework for designing 2D NR materials, but also promote further research in the direction of multifunctional quantum devices for spintronics.