Intrinsic single-layer multiferroics in transition-metal-decorated chromium trihalides

Abstract

Two-dimensional materials possessing intrinsic multiferroic properties have long been sought to harnessing the magnetoelectric coupling in nanoelectronic devices. Here, we report the achievement of robust type Ⅰ multiferroic order in single-layer chromium trihalides by decorating transition metal atoms. The out-of-plane ferroelectric polarization exhibits strong atomic selectivity, where 12 of 84 single-layer transition metal-based multiferroic materials possess out-of-plane ferroelectric or antiferroelectric polarization. Group theory reveals that this phenomenon is strongly dependent on p-d coupling and crystal field splitting. Cu decoration enhances the intrinsic ferromagnetism of trihalides and increases the ferromagnetic transition temperature. The magnetoelectric coupling in this system is studied by calculating the electric polarization of different ferroelectric structures (antiferroelectric and ferroelectric). Moreover, both ferroelectric and antiferroelectric phases are obtained, providing opportunities for electrical control of magnetism and energy storage and conversion applications. Furthermore, the transport properties of Cu(CrBr₃)₂ devices are calculated based on the nonequilibrium Green's function, and the results demonstrate outstanding spin filtering properties and a low-bias negative differential resistance effect for low power consumption. Our findings not only increase the understanding of two-dimensional multiferroic materials and demonstrate out-of-plane ferroelectric polarization but also reveal the mechanism of the emerging ferroelectricity and enhanced ferromagnetism, with promising applications in nanosized electronic and spintronic devices.