  Nowadays, designing and searching for materials with multiple functional
characteristics are the key to achieving high-performance electronic devices.
Among many candidates, two-dimensional multiferroic materials have great
potential to be applied in highly-integrated magnetoelectric devices, such as
high-density non-volatile memories. Here, we predict a two-dimensional material
VOF2 monolayer to possess intrinsic ferroelectric and ferromagnetic properties.
The VOF$_2$ monolayer own the largest in-plane ferroelectric polarization
($332$ pC/m) in the family of VO$X_2$ ($X$: halogen) oxyhalides. Different from
other VO$X_2$ monolayers whose magnetic ground states are antiferromagnetic or
noncollinear spiral textures, the VOF$_2$ monolayer owns a robust ferromagnetic
ground state, which is rare but highly desirable. Our theoretical prediction
provides a good candidate and starting point for the further pursuit of more
two-dimensional multiferroic materials with high-performance
magnetoelectricity.
