First-Principles Investigation of Magnetoelectric Coupling in 2D Ferromagnetic Janus Nanomaterials for Nonvolatile Memory Applications

Multiferroic materials, which exhibit both ferromagnetic and ferroelectric properties, are promising for nonvolatile memory applications owing to their multifunctionality. Conventional type-II multiferroic materials rely on chiral magnetic orders to break the inversion symmetry and generate ferroelectricity. Recent studies have revealed chiral spin orders and spin-induced ferroelectricity in layered materials and their monolayers. Here, we explored the spin-induced in-plane ferroelectricity in a series of ferromagnetic transition metal dihalides with the Janus structure. The broken inversion symmetry due to the Janus structure results in permanent out-of-plane electric polarization. Using first-principles calculations, we predicted in-plane ferroelectricity in these materials. The direction (and magnitude for some materials) of in-plane electric polarization depended on the direction of in-plane magnetization, reflecting a unique magnetoelectric coupling in magnetic Janus materials. This work provides a 2D material system for magnetic control of ferroelectricity. Our results demonstrate that Janus TXY monolayers are promising candidates for high-performance nonvolatile memory and multifunctional devices.