Magnetoelectric effects in ferromagnetic metal monolayers

Manipulating magnetic properties by purely electrical means is a key challenge to improve information technology. In the three-dimensional ferromagnetic (FM) metal thin films, for example, the 3d-transitonal metal thin films Fe, Co, and Ni, the electric-field effect is restricted within the surface around 2-3 Å due to the screening effect, and it is hard to separate the bulk and surface states. In the present investigation, through first-principles calculations, we explore the electric-field effect on the two-dimensional (2D) FM metal monolayers Fe₃GeTe₂, Fe₃GeSe₂, and Fe₃GeTeSe. It is found that magnetic anisotropy energy (MAE) of these three materials follows the sequence: Fe₃GeTe₂ > Fe₃GeTeSe > Fe₃GeSe₂, because the atomic spin-orbital coupling of Te is much stronger than that of Se. The most interesting finding is that the electric-field effect on MAE is obviously enhanced in Fe₃GeTeSe, which is nearly ten times of Fe₃GeTe₂ and Fe₃GeSe₂, and we find the large difference results from its asymmetric structure. Our investigation reveals the magnetoelectric (ME) mechanism and obtains the large ME effect, which is of great significance in the 2D magnetoelectronics.