Large‐Spin‐Gap Nodal‐Line Half‐Metal and High‐Temperature Ferromagnetic Semiconductor in Cr₂X₃ (X=O,S,Se) Monolayers

Abstract

Abstract Two‐dimensional (2D), high‐temperature, half‐metal ferromagnetic semiconductors with large spin gap and topological band structures are highly desirable for novel nanoscale spintronic applications. A family of stable 2D honeycomb‐Kagome Cr 2 X 3 (X=O,S,Se) monolayers is proposed through first‐principles calculations. Buckled Cr 2 O 3 is a ferromagnetic semiconductor with large out‐of‐plane magnetocrystalline anisotropy energy and a predicted Curie temperature of 332 K under moderate biaxial tensile strain. Planar Cr 2 S 3 and Cr 2 Se 3 are ferromagnetic half‐metals with mirror‐symmetry‐protected nodal lines for spin‐down channel and large direct gap (4.59 and 4.76 eV) for spin‐up channel. The Fermi velocities for Cr 2 S 3 and Cr 2 Se 3 are 2.1×10 5 and 1.5×10 5 m s −1 , respectively, which is comparable with that of silicene, 5.3 × 10 5 m s −1 . Their Berezinskii–Kosterlitz–Thouless transition temperatures are determined to be as high as 445 and 695 K. In addition, their half metallicity can be well maintained on h‐BN nanosheets and is immune to chemical perturbation and mechanical strain. Its fascinating magnetic properties and topological nodal lines render 2D Cr 2 X 3 (X=O,S,Se) suitable for novel spintronic devices and exotic quantum applications.