First-principles investigation of two-dimensional iron molybdenum nitride: A double transition-metal cousin of MoSi₂N₄(MoN) monolayer with distinctive electronic and topological properties

As the homologous compounds of MoSi₂N₄, the MoSi₂N₄(MoN)_n monolayers have been synthesized in a recent experiment. These systems consist of homogeneous metal nitride multilayers sandwiched between two SiN surfaces, which extends the septuple-atomic-layer MSi₂N₄ system to ultra-thick MSi₂N₄(MN)_n forms. In this paper, we perform a first-principles study on the MoSi₂N₄(FeN) monolayer, which is constructed by iron molybdenum nitride intercalated into the SiN layers. As a cousin of MoSi₂N₄(MoN), this double transition-metal system exhibits robust structural stability from the energetic, mechanical, dynamical and thermal perspectives. Different from the MoSi₂N₄(MoN) one, the MoSi₂N₄(FeN) monolayer possesses intrinsic ferromagnetism and presents a bipolar magnetic semiconducting behaviour. The ferromagnetism can be further enhanced by the surface hydrogenation, which raises the Curie temperature to 310 K around room temperature. More interestingly, the hydrogenated MoSi₂N₄(FeN) monolayer exhibits a quantum anomalous Hall (QAH) insulating behaviour with a sizeable nontrivial band gap of 0.23 eV. The nontrivial topological character can be well described by a two-band k · p model, confirming a non-zero Chern number of C = 1. Similar bipolar magnetic semiconducting feature and hydrogenation-induced QAH state are also present in the WSi₂N₄(FeN) monolayer. Our study demonstrates that the double transition-metal MSi₂N₄(M′N) system will be a fertile platform to achieve fascinating spintronic and topological properties.