  CrI$_{2}$ is a quasi-one dimensional (1D) van der Waals (vdW) system that
exhibits helimagnetism that propagates along the ribbons. This was determined
from neutron time-of-flight diffraction measurements. Below $T_N=17$ K, a
screw-like helimagnetic order develops with an incommensurate wavevector of
$\mathbf{q} \approx (0.2492,0,0)$ at 8 K. Using density functional theory
(DFT)$+U$ calculations, the $J_{1}$-$J_{2}$ model was leveraged to describe the
helimagnetism, where $J_{1} (> 0)$ and $J_2 (< 0)$ correspond, respectively, to
a ferromagnetic nearest neighbor (NN) and antiferromagnetic next-nearest
neighbor (NNN) intrachain interaction. The DFT$+U$ calculations predict that
bulk CrI$_2$ in the orthorhombic $Cmc2_1$ crystal structure satisfies the
$|J_2| > |J_1|/4$ condition, which favors formation of helimagnetic order.
