Electronic and magnetic properties of Janus monolayer Al ₂ SO modified by defects and doping: a first-principles study

In recent years, two-dimensional (2D) Janus structures have attracted great research attention because of their promise for practical applications. In this work, Janus monolayer Al₂SO under the effects of vacancy and doping is systematically investigated. The pristine Al₂SO monolayer exhibits a direct-gap semiconductor nature with a band gap of 1.52 eV. The chemical bonds Al1-O and Al2-S are predominantly ionic, meanwhile the covalent character dominates the Al1-Al2 bond. A single Al2 vacancy induces a half-metallic nature with a total magnetic moment of 1.00 <i>μ</i> _B, meanwhile no magnetism is obtained by creating a single Al1 vacancy that metallizes the monolayer. The nonmagnetic semiconductor nature is preserved with single O and S vacancies, which tune the band gap to 1.41 and 1.70 eV, respectively. Significant magnetism with an overall magnetic moment of 5.00 <i>μ</i> _B is induced by doping with a single Fe atom. Our simulations assert the antiferromagnetic semiconductor nature of the Fe-doped Al₂SO monolayer, where antiferromagnetism is more stable in the case of pair-Fe-atom substitution with an energy difference of 309.3 meV compared to ferromagnetism. Beyond monoelement doping, the substitution of small clusters of FeN₃ and FeF₃ is also investigated. These clusters induce a feature-rich electronic nature with total magnetic moments of 2.00 and 2.11 <i>μ</i> _B, respectively. In all cases, Fe atoms mainly induce the magnetic moment in the system. Small cluster doping also generates multiple mid-gap energy states around the Fermi level, which is crucial to control the electronic nature of the system. Our study provides new insights into the functionalization of the Janus monolayer Al₂SO that could be employed to make new promising 2D spintronic materials.