Robust magnetic behavior in two-dimensional GaN caused by atomic vacancies

Point defect introduction is an important method for inducing robust unconventional magnetic behaviors. Here, we studied the effects of atomic vacancies, including Ga (VGa) and N vacancies (VN), on the magnetic properties of two-dimensional (2D) planar and buckled GaN based on density functional theory (DFT). The results demonstrate that the introduction of VGa causes nonzero magnetic moments in 2D planar and buckled GaN, while VN does not. Furthermore, for the planar structure, distinct magnetic behaviors occur in two different VGa ratio regions. Notably, when the VGa ratio is greater than 1/16 (1 Ga vacancy per 16 Ga atoms), 2D planar GaN exhibits a half-metallic nature, and its spin polarization at the Fermi level reaches 100%. Utilizing 2D planar GaN with high VGa ratios as ferromagnetic layers, a magnetic tunnel junction with an ultra-high spin filtering effect at the Fermi level can be obtained. On the other hand, the planar structure with a low vacancy ratio (less than about 1/16) remains semiconductive. In this structure, we found that the band gap increases with decrease in VGa ratio. As for 2D buckled GaN, it exhibits a VGa–dependent nonzero band gap for any VGa ratio. In this case, the band gap can be tuned by varying the VGa ratio.