Two dimensional (2D) materials are currently attracting considerable interest due to their promising applications in future nanoelectronic devices. Magnetic 2D materials are also gaining attention, for their possible use in novel spintronic devices [1]. Recently, hole-doping in monolayer SnO has been theoretically predicted to induce a paramagnetic to ferromagnetic phase transition in this 2D material, for a typical hole density of about 5x10¹³/cm² [2]. Magnetism in monolayer SnO arises from an exchange splitting of electronic states at the top of the valence band, where the density of states exhibits a sharp van Hove singularity, resulting in a so-called Stoner (magnetic) instability [2]. This behavior is typical of materials with “Mexican-hat” energy band edges (as predicted for the valence band edge of monolayer SnO), and has also been predicted in e.g. monolayer GaSe [3].

In this work, the possibility to induce hole doping in monolayer SnO by intrinsic and extrinsic defects is investigated, using first-principles simulations, based on density functional theory. It is found that Sn vacancies generate spin-polarized gap states near the valence band edge of monolayer SnO, and that these point defects are behaving like acceptors. A typical density of 5x10¹³/cm² of Sn vacancies induces a paramagnetic to ferromagnetic phase transition in the material, with a magnetic moment density of 1 Bohr magneton/hole. Substitutional doping of Sn atoms by e.g. In or Zn atoms is also predicted to result in hole-doping of monolayer SnO, and also leads to a ferromagnetic order in the 2D material. The possibility to induce a ferromagnetic phase transition in monolayer SnO by electrostatic doping will also be discussed.

[1] W. Han, APL Mater. 4, 032401 (2016).

[2] L. Seixas et al., Phys. Rev. Lett. 116, 206803 (2016).

[3] T. Cao et al., Phys. Rev. Lett. 114, 236602 (2015).