  Multiferroic materials with coupled ferroelectric and ferromagnetic
properties are important for multifunctional devices due to their potential
ability of controlling magnetism via electric field, and vice versa. The recent
discoveries of two-dimensional ferromagnetic and ferroelectric materials have
ignited tremendous research interest and aroused hope to search for
two-dimensional multiferroics. However, intrinsic two-dimensional multiferroic
materials and, particularly, those with strong magnetoelectric couplings are
still rare to date. In this paper, using first-principles simulations, we
propose artificial two-dimensional multiferroics via a van der Waals
heterostructure formed by ferromagnetic bilayer chromium triiodide (CrI3) and
ferroelectric monolayer Sc2CO2. In addition to the coexistence of
ferromagnetism and ferroelectricity, our calculations show that, by switching
the electric polarization of Sc2CO2, we can tune the interlayer magnetic
couplings of bilayer CrI3 between ferromagnetic and antiferromagnetic states.
We further reveal that such a strong magnetoelectric effect is from a dramatic
change of the band alignment induced by the strong build-in electric
polarization in Sc2CO2 and the subsequent change of the interlayer magnetic
coupling of bilayer CrI3. These artificial multiferroics and enhanced
magnetoelectric effect give rise to realizing multifunctional nanoelectronics
by van der Waals heterostructures.
