Magnetic and electronic properties of 2D TiX (X = F, Cl, Br and I).

Searching for two-dimensional (2D) materials with a high phase-transition temperature and magnetic anisotropy is critical to the development of spintronics. Herein, we investigate the electronic and magnetic properties of 2D TiX (X = F, Cl, Br and I) monolayers based on density-functional theory (DFT). We show that the 2D TiX monolayers are stable dynamically and thermodynamically as evidenced by phonon and molecular dynamics calculations, respectively, and show their semiconducting nature. We find that the TiBr and TiI monolayers are ferromagnetic with magnetic anisotropy out of plane, which are intrinsic without the need for external intervention. The magnetic anisotropy energies of the TiBr and TiI monolayers are 0.8 and 2.5 meV per s.f., respectively. The Curie temperatures of TiBr and TiI are 75 K and 90 K, respectively. We further show that the interlayer magnetic coupling and magnetic anisotropy energies (MAE) of the bilayer TiI can be tuned by the interlayer distance. Additionally, a two-step transition in the magnetic state is observed in the bilayer TiI with AB' stacking under applied strain in a vertical direction. It is expected that our design may enrich two-dimensional functional materials, which may find versatile applications.