  Bimetal transition iodides in two-dimensional scale provide an interesting
idea to combine a set of single-transition-metal ferromagnetic semiconductors
together. Motivated by structural engineering on bilayer CrI$_3$ to tune its
magnetism and works that realize ideal properties by stacking van der Waals
transitional metal dichalcogenides in a certain order. Here we stack monolayer
VI$_3$ onto monolayer CrI$_3$ with a middle-layer I atoms discarded to
construct monolayer V$_2$Cr$_2$I$_9$. Based on this crystal model, the stable
and metastable phases are determined among 7 possible phases by
first-principles calculations. It is illustrated that both the two phases have
Curie temperature $\sim$ 6 (4) times higher than monolayer CrI$_3$ and VI$_3$.
The reason can be partly attributed to their large magnetic anisotropy energy
(the maximum value reaches 412.9 $\mu$eV/atom). More importantly, the Curie
temperature shows an electric field and strain dependent character and can even
surpass room temperature under a moderate strain range. At last, we believe
that the bimetal transition iodide V$_2$Cr$_2$I$_9$ monolayer would support
potential opportunities for spintronic devices.
