Emerging two-dimensional half-metal with high Curie temperature and strain-tunable altermagnetism

To achieve room-temperature high spin polarization and pursue potential applications in high-performance spintronic device, the study of two-dimensional (2D) half-metallic materials is of great interest. Here, by employing first-principles calculations, we have predicted a stable 2D monolayer ferromagnetic half-metal ${\mathrm{Mn}}_{2}{\mathrm{Se}}_{2}\mathrm{O}$, exhibiting a high Curie temperature of nearly 467 K, a sizable in-plane magnetic anisotropy ($306\phantom{\rule{4pt}{0ex}}\textmu{}\mathrm{eV}/\mathrm{Mn}$), and a wide spin gap of 2.0 eV. Notably, an exotic magnetic phase transition from ferromagnetism to altermagnetism is predicted by applying a moderate compressive strain, while the half-metallic ferromagnetic ordering of the ${\mathrm{Mn}}_{2}{\mathrm{Se}}_{2}\mathrm{O}$ monolayer is robustly retained under tensile strains. Furthermore, the half-metallicity of the ${\mathrm{Mn}}_{2}{\mathrm{Se}}_{2}\mathrm{O}$ monolayer makes it an ideal electrode candidate that is used in the magnetic tunnel junction with a colossal tunnel magnetoresistance ratio of about ${10}^{12}%$. Our findings not only expand the comprehensive understanding of a 2D room-temperature ferromagnet with promising spintronics electrode application, but they also offer a potential avenue for designing magnetomechanical coupling spintronic devices.