Electric Field-Modulated Magnetic Phase Transition in van der Waals CrI₃ Bilayers

Two-dimensional van der Waals (vdW) magnetic materials are well-recognized milestones toward nanostructured spintronics. An interesting example is CrI₃; its magnetic states can be modulated electrically, allowing spintronics applications that are highly compatible with electronics technologies. Here, we report the electric field alone induces the interlayer antiferromagnetic-to-ferromagnetic (AFM-to-FM) phase transition in CrI₃ bilayers with critical field as low as 0.12 V/Å. The AFM-FM energy difference ΔE increases with electric field and is closely related to the field-induced on-site energy difference defined as the splitting between the electronic states of the two vdW layers. Our tight-binding model fits closely with ΔE as a function of electric field and gives a consistent estimation for orbital hopping, exchange splitting, and crystal field splitting. Furthermore, a CrI₃-based spin field-effect device is suggested with the spin current switched on and off solely by the electric field. These findings not only reveal the physics underlying the transition but also provide guidelines for future discovery and design.