We present first-principles results on the structural, electronic, and magnetic properties of a new family of two-dimensional antiferromagnetic (AFM) manganese chalcogenides, namely, monolayer $\mathrm{Mn}X$ and Janus $X\mathrm{Mn}Y$ ($X,Y=\mathrm{S}$, Se, Te), among which monolayer MnSe was recently synthesized in experiments [Aapro et al., ACS Nano 15, 13794 (2021)]. By carrying out calculations of the phonon dispersion and ab initio molecular dynamics simulations, we first confirmed that these systems, characterized by an unconventional strongly-coupled-bilayer atomic structure [consisting of Mn atoms buckled to chalcogens forming top and bottom ferromagnetic (FM) planes with antiparallel spin orientation], are dynamically and thermally stable. The analysis of the magnetic properties shows that these materials have robust AFM order, retaining a much lower energy than the FM state even under strain. Our electronic structure calculations reveal that pristine $\mathrm{Mn}X$ and their Janus counterparts are indirect-gap semiconductors, covering a wide energy range and displaying tunable band gaps by the application of biaxial tensile and compressive strain. Interestingly, owing to the absence of inversion and time-reversal symmetry, and the presence of an asymmetrical potential in the out-of-plane direction, Janus $X\mathrm{Mn}Y$ become spin-split gapped systems, presenting a rich physics yet to be explored. Our findings provide insights into this physics and highlight the potential for these two-dimensional manganese chalcogenides in AFM spintronics.

中文翻译：

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MonolayerMnXand JanusXMnY(X,Y=S, Se, Te)：二维反铁磁半导体家族

我们提出了关于一个新的二维反铁磁 (AFM) 锰硫族化物家族的结构、电子和磁特性的第一性原理结果，即单层$锰X$和杰纳斯$X锰\mathrm{是的}$($X,\mathrm{是的}=\mathrm{小号}$, Se, Te)，其中最近在实验中合成了单层 MnSe [Aapro等人。, ACS Nano 15 , 13794 (2021)]。通过计算声子色散和从头算分子动力学模拟，我们首先证实了这些系统，其特征在于非常规的强耦合双层原子结构 [由 Mn 原子屈曲到形成顶部和底部铁磁 (FM) 平面的硫属元素组成具有反平行自旋方向]，是动态和热稳定的。磁性分析表明，这些材料具有稳健的 AFM 阶，即使在应变下也能保持比 FM 状态低得多的能量。我们的电子结构计算表明，原始$锰X$和它们的 Janus 对应物是间接带隙半导体，覆盖了很宽的能量范围，并通过应用双轴拉伸和压缩应变显示出可调节的带隙。有趣的是，由于不存在反演和时间反转对称性，以及在面外方向上存在不对称势能，Janus$X锰\mathrm{是的}$成为自旋分裂间隙系统，呈现出丰富的物理学尚待探索。我们的研究结果提供了对该物理学的见解，并突出了这些二维锰硫属化物在 AFM 自旋电子学中的潜力。