Manipulating the electronic structure and physical properties in monolayer Mo 2 I 3 Br 3 via strain and doping.

Identifying new two-dimensional intrinsic ferromagnets with high transition temperatures is a key step of improving device performance. Here we used first-principles calculations to demonstrate that the monolayer Janus Mo 2 I 3 Br 3 is an intrinsic ferromagnetic bipolar semiconductor with a large out-of-plane spin orientation. The calculated phonon dispersion and ab initio molecular dynamic simulations indicate the stability dynamically and thermally. Furthermore, we investigated the effect of electrostatic doping or in-plane biaxial strain on the electronic structures and magnetic and optical properties of monolayer Mo 2 I 3 Br 3 . We find that the magnetic anisotropy energy and Curie temperature are enhanced more than 4 and 2 times with the hole doping compared with those in the pristine monolayer Mo 2 I 3 Br 3 , respectively. The calculated electronic structures show that the stable half-metallic states are formed by electron or hole doping due to the strong spin polarization of the electronic states around the Fermi level. Furthermore, the spin orientation in the metallic channel of the doped monolayer Mo 2 I 3 Br 3 can be flipped with the increase of electron doping concentration. In addition, the magnetic anisotropy energy and Curie temperature can also be effectively manipulated by in-plane biaxial strain. The spin polarization of the conduction band minimum can be reversed by the tensile strain of 3% for the monolayer Mo 2 I 3 Br 3 , transforming it into an indirect band gap semiconductor. Finally, the calculated large and tunable optical absorption coefficient indicates that monolayer Mo 2 I 3 Br 3 is a promising candidate for potential optoelectronic applications. Our results may open up more opportunities for few-layer van der Waals crystals in magnetic storage, spintronics, and optoelectronic devices.