MnNBr Monolayer: A High‐Temperature Ferromagnetic Half‐Metal with Type‐II Weyl Fermions

Abstract

For spintronics, it is highly desirable to obtain stable low‐dimensional materials with ferromagnetic ground state, 100% spin polarization, and high Curie temperature. Moreover, type‐II Weyl fermions are also desired for realizing high‐speed anisotropic transport. Herein, based on first‐principles calculations, the orthorhombic MnNBr monolayer is identified as a needed ferromagnetic half‐metal, which not only has a high Curie temperature (910 K), but also holds type‐II Weyl state with Lorentz symmetry broken. Analysis of the stability reveals that the MnNBr monolayer is energetically, mechanically, dynamically, and thermally stable. Remarkably, in the vicinity of the Fermi level there exist both type‐I and titled type‐II Weyl states, whose nodes form continuously distributed Weyl loops. Under intrinsic out‐of‐plane magnetization, they are robust against spin–orbital coupling due to the protection of glide mirror symmetry. Moreover, near the type‐II Weyl point, there is direction‐dependent band dispersion: the largest fermion velocities can be found in the k path of G–X (up to 6.86 × 105 m s−1), while quasi‐flat bands with negligible band dispersion can be found along the direction being parallel to G–Y. This indicates that MnNBr monolayer should be a promising candidate for further applications of high‐speed anisotropic transport and studies of strongly correlated electronic states.