  Following the recent isolation of monolayer CrI3, there has been a surge of
new two-dimensional van der Waals magnetic materials, whose incorporation in
van der Waals heterostructures offers a new platform for spintronics, proximity
magnetism, and quantum spin liquids. A primary question in this burgeoning
field is how exfoliating crystals to the few-layer limit influences their
magnetism. Studies on CrI3 have shown a different magnetic ground state for
ultrathin exfoliated films but the origin is not yet understood. Here, we use
electron tunneling through few-layer crystals of the layered antiferromagnetic
insulator CrCl3 to probe its magnetic order, finding a ten-fold enhancement in
the interlayer exchange compared to bulk crystals. Moreover, temperature- and
polarization-dependent Raman spectroscopy reveal that the crystallographic
phase transition of bulk crystals does not occur in exfoliated films. This
results in a different low temperature stacking order and, we hypothesize,
increased interlayer exchange. Our study provides new insight into the
connection between stacking order and interlayer interactions in novel
two-dimensional magnets, which may be relevant for correlating stacking faults
and mechanical deformations with the magnetic ground states of other more
exotic layered magnets, such as RuCl3.
