  The emergence of two-dimensional (2D) magnetic crystals and moir\'e
engineering has opened the door for devising new magnetic ground states via
competing interactions in moir\'e superlattices. Although a suite of
interesting phenomena, including multi-flavor magnetic states, noncollinear
magnetic states, moir\'e magnon bands and magnon networks, has been predicted,
nontrivial magnetic ground states in twisted bilayer magnetic crystals have yet
to be realized. Here, by utilizing the stacking-dependent interlayer exchange
interactions in CrI3, we demonstrate in small-twist-angle bilayer CrI3 a
noncollinear magnetic ground state. It consists of both antiferromagnetic (AF)
and ferromagnetic (FM) domains and is a result of the competing interlayer AF
coupling in the monoclinic stacking regions of the moir\'e superlattice and the
energy cost for forming AF-FM domain walls. Above the critical twist angle of ~
3{\deg}, the noncollinear state transitions abruptly to a collinear FM ground
state. We further show that the noncollinear magnetic state can be controlled
by gating through the doping-dependent interlayer AF interaction. Our results
demonstrate the possibility of engineering moir\'e magnetism in twisted bilayer
magnetic crystals, as well as gate-voltage-controllable high-density magnetic
memory storage.
