A Novel van der Waals Ferromagnetic Semiconductor*

The discovery of long-range magnetic ordering in two-dimensional (2D) materials has posed both challenges and opportunities, revealing novel physical phenomena. These materials, featuring spin-polarized electrons/holes and atomic layer thickness, underpin advanced information technology with high integration, ultra-fast response, and low power consumption. Monolayer CrI₃, as a demonstrated member of this family [1], displays adjustable interlayer magnetic coupling, rendering it highly favorable for spintronic applications. Similarly, the centrosymmetric structure of Cr₂Ge₃Te₆, functioning as a ferromagnetic semiconductor [2], presents diverse opportunities for the creation of 2D magneto-electric devices and magneto-optic applications. In this study, inspired by recent findings, we conducted a comprehensive investigation into the electronic and magnetic properties of monolayer VClBr₂ [3] using first-principles density functional theory. This material represents a novel form of an intrinsic ferromagnet in the two-dimensional realm, displaying semiconducting traits. Under strain ranging from -1% to 5%, it maintains consistent ferromagnetic (FM) characteristics. A shift to antiferromagnetic (AFM) phase occurs between -5% and -1% strain. When exposed to an electric field (E_z = 2.5 V/nm), VClBr₂ displays FM ordering, transitioning to AFM when the field increases from E_z = 5 V/nm to 10 V/nm.

Remarkably, without any defects or changes in chemical composition, we observed a transition in the material from semiconductor to metal to half-metal based on the ferromagnetic and antiferromagnetic ground states, influenced by strain engineering and an electric field. When an electric field was applied along the z-axis at 2.5 V/nm, the Curie temperature (T_c) drastically increased to approximately 340 K, marking a substantial enhancement of about 6700% from its base value. Additionally, our calculations on magneto anisotropic energy (MAE) confirmed the presence of an in-plane easy axis, with a magnetization of 2.85 µ_B/V atom.