Intercalation-induced high-temperature multiferroicity with strong magnetoelectric coupling in 2 <i>H</i> -VSe2 bilayer

Two-dimensional (2D) materials with a coexistence of magnetic and ferroelectric (FE) orders (i.e., multiferroics) provide a promising approach to control magnetism by electric fields. However, 2D multiferroic materials with concurrent strong magnetoelectric (ME) coupling and high transition temperature are rare. Here, we propose to realize multiferroicity in the existing 2D van der Waals (vdW) magnetic materials by intercalation with nonmagnetic ds-block element, taking Cu-intercalated 2H-VSe2 bilayer as a prototype. Intercalated ds-block element preferentially occupies the tetrahedral sites within the vdW gap. This not only breaks the space inversion symmetry of the host material, inducing spontaneous electric polarization, but also transfers different carrier density to adjacent magnetic layers, triggering layer-dependent magnetic evolution. Although the FE polarization and magnetic orders arise from different sources, the layer-dependent change of magnetism is driven by ferroelectricity, exhibiting strong ME coupling. Moreover, Cu atoms migrate between two degenerate tetrahedral sites with a moderate barrier, acting as a new knob to control the electric polarization and magnetization simultaneously. By tuning Cu concentration, room-temperature 2D multiferroicity can be realized. We expect that intercalation of nonmagnetic ds-block element could be a general way to realize strong ME coupling and high-temperature multiferroicity in 2D vdW magnetic materials.