Ferroelectric Control of Magnetism and Giant Magnetoresistance Via Intercalation-Induced Symmetry Breaking in Two-Dimensional Multiferroics with Strong Magnetoelectric Coupling

The discovery of two-dimensional (2D) multiferroics with strong magnetoelectric (ME) coupling is crucial to spintronics. However, the independent origins of ferroelectricity and magnetism restrict the number of 2D multiferroics and hinder their practical applications. Here, via density functional theory combined with nonequilibrium Green's functions, we propose a 2D A-type fully compensated ferrimagnetic metal Cr₄S₄FBr₂ through ion intercalation. Monolayer Cr₄S₄FBr₂ demonstrates a high Néel temperature and a ferroelectric-paraelectric transition temperature exceeding room temperature, together with considerable nonrelativistic spin splitting and strong ME coupling. Notably, reversal of the electric polarization fully inverts the spin polarization orientation, reverses spin textures, and alters the gap Chern number from -2 to +2. In a multiferroic tunneling junction, Cr₄S₄FBr₂ enables magnetoresistance up to 4.8 × 10³% and highly spin-polarized current at low bias, controlled solely by electric polarization switching. Our results establish a new avenue for electric-field-mediated ME control and guide the design of high-performance multiferroics.