Sliding ferroelectricity (SFE) found in two-dimensional (2D) van der Waals (vdW) materials, such as BN and transition-metal dichalcogenides bilayers, opens an avenue for 2D ferroelectric materials. Multiferroic coupling in 2D SFE materials brings us an alternative concept for spintronic memory devices. In this study, using first-principles calculations, we demonstrate that MnSe multilayers constructed by the recently-synthesized MnSe monolayer have large sliding-driven reversible out-of-plane electric polarization (~10.6 pC m−1) and moderate interlayer sliding barriers superior to the existing 2D SFE materials. Interestingly, the intrinsic electric polarization is accompanied by nonzero net magnetic moments which are also switchable via lateral interlayer sliding. Additionally, both SFE and magnetoelectric coupling can be effectively regulated by external strain and/or hole doping. Our findings suggest the potential of MnSe multilayers in 2D multiferroic and spintronic applications.

Two-dimensional (2D) multiferroic materials offer a unique platform for the development of next-generation multifunctional devices. Based on first-principles calculations, a stable 2D configuration of a lead oxide (δ-PbO) monolayer is proposed to realize the multiferroic coupling between ferroelectricity (FE) and ferroelasticity (FA). The δ-PbO monolayer has a spontaneous in-plane polarization of about 2.64 × 10 −10 C/m whose orientation can be reversed by overcoming a low energy barrier of 27.5 meV/atom. The interplay between FE and FA enables the switch of the electric polarization direction by 90°. Moreover, the mechanical properties of the δ-PbO monolayer exhibit significant in-plane anisotropy accompanied by a large negative Poisson's ratio of about −0.68. The coexistence of auxeticity and multiferroicity in this 2D material renders a promising strategy to regulate the mechanical and electronic properties and the interplay between them and thereby concepts for nanoscale devices.

Sliding ferroelectricity (SFE) found in two-dimensional (2D) van der Waals (vdW) materials, such as BN and transition-metal dichalcogenides bilayers, open an avenue for 2D ferroelectric materials. The multiferroic coupling in 2D SFE materials is expected to bring about new concepts for spintronic memory devices. Here, using first-principles calculations, we demonstrate that the recently-synthesized MnSe multilayers [ACS Nano 15, 13794 (2021)] have large reversible out-of-plane electric polarization (~10.6 pC/m) and moderate interlayer sliding barriers superior to the existing 2D SFE materials. More interestingly, the intrinsic electric polarization is also accompanied by nonzero net magnetic moments whose direction is dependent on the electric polarization direction and thus can be switched by interlayer sliding. Additionally, both the SFE and magnetoelectric coupling can be effectively regulated by external strain and/or hole doping. Our findings suggest the potential of MnSe multilayers in 2D multiferroic and spintronic applications.