Exotic magnetism in As-doped α/β-InSe monolayers with tunable anisotropic carrier mobility.

The two-dimensional (2D) material family is expanding fast as novel metal chalcogenides are being continually fabricated and intriguingly, plenty of them are ideal candidates for future nanoscale electronic and magnetic devices. Based on first-principles calculations, we investigated the electronic and magnetic properties of α/β-InSe monolayers. We find singularities of density of states appear in the valence band and hole doping (such as a Se atom substituted by a lower valence atom) can induce various ferromagnetic phase transitions in the α/β-InSe monolayers. In particular, replacement by arsenic at the anion site can enhance ferromagnetism and drive α-InSe to be a robust half-metal and β-InSe to be a bipolar magnetic semiconductor. Then, we proposed spin-polarized field-effect transistors based on α-InSe and a bipolar field-effect spin-filter based on β-InSe. Besides, we also discussed the influences of the molecules in air on the device performance such as carrier mobility. We found that the adsorption of either O or HO on α/β-InSe induced changes in hole mobility in different directions. These findings reveal a new road to electronic and magnetic modulations in 2D materials.