Modeling magnetism and electric field effects in 2D chromium iodide

As conventional transistors reach their limit, 2D materials are becoming a prime focus in developing next-generation quantum devices, such as tunneling field-effect transistors. The magnetic properties in spintronic materials can be controlled by applying an electric field in a process known as gating.

Cheng et al. used first principles to model and simulate the electric gate effects on 2D chromium iodide (CrI₃) sandwiched between graphene and hexagonal boron nitride (h-BN).

When the dimension of CrI₃ reduces from 3D to 2D, the local Coulomb interaction increases by about 1 electron volt and goes from being ferromagnetic to antiferromagnetic (AFM). As a 2D material, CrI₃ exhibits antiferromagnetic (AFM) interlayer coupling that can be tuned by the application of magnetic field, gate electric field or pressure.

The authors compared bare bilayer CrI₃ using interlayer combinations of graphene, known for its extraordinary conducting properties, and h-BN, an insulator. They found that inserting bilayer CrI₃ between two graphene sheets prohibits a magnetic phase transition in relatively low electric fields due to electrostatic shielding.

However, if bilayer CrI₃ is placed between a graphene sheet as the top layer and an h-BN sheet as the bottom layer, it became possible to drive a magnetic phase transition using an electric field, although it still requires a larger field than that for bare bilayer CrI₃. Before the magnetic phase transition, the magnetic moment in the AFM state increases at a smaller electric field due to charge transfer between graphene and bilayer CrI₃.

The researchers plan to next investigate electron tunneling in the same materials.

Source: “First-principles study of magnetism and electric field effects in 2D systems,” by Hai-Ping Cheng, Shuanglong Liu, Xiao Chen, Long Zhang, and James N. Fry, AVS Quantum Science (2020). The article can be accessed at https://doi.org/10.1116/5.0009316 .