  Comparing with the widely known transitional metal based van der Waals (vdW)
materials, rare-earth based ones are rarely explored in the research of
intrinsic two-dimensional (2D) magnetism. In this work, we report the physical
properties of DyOCl, a rare-earth based vdW magnetic insulator with direct band
gap of $\sim 5.72~eV$. The magnetic order of bulk DyOCl is determined by
neutron scattering as the $A$-type antiferromagnetic structure below the
N\'{e}el temperature $T_N=10~$K. The large magnetic moment near 10.1 $ \mu_{B}
$/Dy lies parallel to the $a$-axis with strong uniaxial magnetic anisotropy. At
$2~K$, a moderate magnetic field ($\sim 2~T$) applied along the easy axis
generates spin-flip transitions and polarizes DyOCl to a ferromagnetic state.
Density functional theory calculations reveal an extremely large magnetic
anisotropy energy ($-5850~\mu eV/Dy$) for DyOCl, indicating the great
potentials to realize magnetism in 2D limit. Furthermore, the mechanical
exfoliation of bulk DyOCl single crystals down to seven layers is demonstrated.
Our findings suggest DyOCl is a promising material playground to investigate 2D
$f$-electron magnetism and spintronic applications at the nanoscale.
