Magnetic and electronic properties of 2D TiX₃ (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 TiX₃ (X = F, Cl, Br and I) monolayers based on density-functional theory (DFT). We show that the 2D TiX₃ monolayers are stable dynamically and thermodynamically as evidenced by phonon and molecular dynamics calculations, respectively, and show their semiconducting nature. We find that the TiBr₃ and TiI₃ monolayers are ferromagnetic with magnetic anisotropy out of plane, which are intrinsic without the need for external intervention. The magnetic anisotropy energies of the TiBr₃ and TiI₃ monolayers are 0.8 and 2.5 meV per s.f., respectively. The Curie temperatures of TiBr₃ and TiI₃ are 75 K and 90 K, respectively. We further show that the interlayer magnetic coupling and magnetic anisotropy energies (MAE) of the bilayer TiI₃ can be tuned by the interlayer distance. Additionally, a two-step transition in the magnetic state is observed in the bilayer TiI₃ 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.