Strain modulated ferromagnetic phase transitions in monolayer FeCl2 through exchange competitions: the first-principle and Monte Carlo simulations

Tunable magnetic phase transitions and novel emergent spin phases in two-dimensional materials are fascinating subjects of research. 1T-FeCl2 has been predicted to be a magnetic monolayer. We performed the first-principle calculations based on density functional theory to clarify the electronic structure and magnetic properties of the monolayer 1T-FeCl2 modulated by the uniaxial and biaxial strains. Based on the stable structure confirmed by the phonon calculations, we showed that the geometry and magnetic structures evolved with strain. In combination with the Monte Carlo simulation, we found that the strain could induce a phase transition between the in-plane ferromagnetic order and the out-of-plane anti-ferromagnetic order. Energy bands with the Hubburd U and spin-orbital couplings confirmed the insulator ground state. We identified the strain-magnetism behavior originating from the competition between the direct-exchange interaction and the super-exchange interaction. Meanwhile, the strains regulated the Curie temperatures by selecting the d–p bonding along the x-direction or y-direction. Through strain engineering, the 1T-FeCl2 could be an intriguing platform for the two-dimensional systems and a potential spintronic material.