Strain-Controllable High Curie Temperature and Magnetic Crystal Anisotropy in a 2D Ferromagnetic Semiconductive FeI₃ Monolayer

The investigation of two-dimensional (2D) intrinsic ferromagnetic (FM) semiconductors (SCs) is a significant focal point in the field of spintronics. The FeI3 monolayer (ML) with intrinsic ferromagnetism was fabricated by density functional theory and confirmed by a global minimum search. The FeI3 ML is a half-semiconductor (HSC) with a band gap of 1.692 eV where FeI3 shows FM order with a Curie temperature (Tc) of 148 K. It shows perpendicular magnetic anisotropy (PMA) and large magnetic anisotropy energy. Moreover, FeI3 shows good dynamic and thermal stability. FeI3 has a Young’s modulus of 35.6 GPa, and biaxial strain could be applied to tune electronic and magnetic properties of FeI3. The band gap, magnetic moment, magnetic exchange parameter (J), and Tc could be effectively controlled by the biaxial strains. It originates from the states near the Fermi-level coming from the contribution of the in-plane atomic orbitals. As the compressive strains increase, FeI3 ML changes from the FM order with PMA into the antiferromagnetic (AFM) state with an in-plane magnetic anisotropy under larger compressive strains (−4.7%). The corresponding critical temperatures, including Tc and Néel temperature (TN), are changed from 148 K (Tc) to 586 K (TN, −10%). Additionally, FeI3 ML changes from HSC to a normal spin-unpolarized SC under larger compressive strains (ε < −4.7%). As tensile strain increases, the energy difference between FM and AFM orders and J monotonously increase as the direct exchange interaction between Fe atoms weakens. The Tc values are also increased to 460 K (10%) and 842 K (16%). Also, FeI3 ML remains HSC with the FM order. The magnetoelectric phase transitions in the strained FeI3 appear, helping researchers to study the controllable magnetoelectric properties of FeI3 in electronic and spintronic equipment.