Prediction of the TiS2 Bilayer with Self-Intercalation: Robust Ferromagnetic Semiconductor with a High Curie Temperature

The search for new two-dimensional magnetic materials has been a hot topic since the discovery of graphene in 2004 as these materials play a crucial role in fields such as spintronics. In this study, we systematically investigated the 2H-TiS₂ bilayer with self-intercalation (SI) of the Ti atom, revealing that SI can introduce magnetism to a nonmagnetic 2H-TiS₂. Taking Ti₁₉S₃₆-AB stacking as an example, we find that 2H–SI–TiS₂ exhibits a ferromagnetic order with a Curie temperature of 377 K. Ti₁₉S₃₆ shows perpendicular magnetic anisotropy, with a magnetic anisotropy energy (MAE) of 7.43 × 10^–2 meV. Additionally, the MAE increases as the self-intercalated Ti’s (Ti_SI) concentration (x) decreases, attributed to the enhanced hybridization interaction between the d_x²–y² and d_xy orbitals of Ti atoms. Ti₁₉S₃₆-AB stacking is identified as a bipolar magnetic semiconductor (BMS) with an indirect band gap of 0.53 eV. As x increases, Ti_mS_n transitions from BMS to half-semiconductor (HSC) and metal and then back to HSC, demonstrating a rich phase. Ti_mS_n shows good dynamic and thermodynamic stabilities at 300 and 500 K, respectively. Furthermore, the formation energy (ε_f) of Ti_mS_n increases monotonically with rising x. Moreover, Ti_mS_n can be easily synthesized under higher μ_Ti. The migration barrier of Ti_SI between adjacent coordination sites is 0.740 eV, further confirming the stability of the self-intercalated structure. These findings imply the potential of 2H-TiS₂ and nonmagnetic transition metal dichalcogenides in spintronics.