  Two-dimensional (2D) ferromagnetic (FM) semiconductors with high Curie
temperature have long been pursued for electronic and spintronic applications.
Here we provide a general strategy to achieve robust FM state in bilayer CrI3
of the monoclinic stacking, which intrinsically has interlayer
antiferromagnetic (AFM) order and weak in-plane FM coupling. We showed that the
proximity effect from bulk semiconducting substrates induces electronic doping
and significantly increases the FM nearest-neighbor exchange for bilayer CrI3,
leading to the AFM-to-FM transition for the interlayer spin configuration as
well as enhanced intralayer FM coupling. By first-principles calculations and
Monte Carlo simulations, bulk and 2D semiconductors providing different
interaction strengths from strong covalent bonding to weak van der Waals (vdW)
interaction with CrI3 are compared to thoroughly address the substrate effect
on magnetic behavior and Curie temperature of bilayer CrI3. These theoretical
results offer a facile route for direct synthesis of 2D ferromagnets on proper
semiconducting substrates to achieve high Curie temperature for device
implementation.
