Stacking induced symmetry breaking and gap opening in Dirac half-metal MnF3†

Abstract

Two-dimensional ferromagnetic materials have a broader development prospect in the field of spintronics. In particular, the high spin polarization system with half-metallic characteristics can be used as an efficient spin injection electrode. Via first-principles calculations, we predict that monolayer MnF₃ has Dirac half-metallic properties. The formation mechanism of this Dirac half-metallic state is mainly attributed to the local symmetry of magnetic Mn³⁺ in the sublattice. It is interesting to note that the local symmetry can be broken in bilayer MnF₃ through different stacking configurations. Therefore, different stacking models of bilayer MnF₃ are established, and the calculation of their magnetic ground states shows that all the systems maintain a ferromagnetic ground state. The AA-stacking holds the symmetry and Dirac electronic states. Under interfacial Coulomb repulsion, the Dirac electronic states of the top layer and bottom layer of MnF₃ are shifted relative to each other and overlap to form a nodal-ring state. Interestingly, in the AB-stacking model, the inversion symmetry exists, while the sublattice symmetry of Mn is broken, resulting in different orbital filling of Mn and forming a large insulating gap (732.2 meV). Additionally, the inversion symmetry of the system is broken in AC-stacking, while the intralayer sublattice symmetry is preserved. Therefore, under the effect of broken inversion symmetry, the Dirac electronic states of both top and bottom layer MnF₃ will have a small gap opening (24.6 meV). The topological properties of all three systems have been analyzed. Based on the above research results, the electronic states of the system can be regulated by changing the stacking model between the 2D magnetic homostructure, which provides an ideal platform for the design and development of spin logic devices.