  Interest in van der Waals materials often stems from a desire to miniaturise
existing technologies by exploiting their intrinsic layered structure to create
near atomically-thin components that do not suffer from surface defects. One
appealing property is easily-switchable yet robust magnetic order, a quality
only sparsely demonstrated in the case of in-plane anisotropy. In this work, we
use widefield nitrogen-vacancy (NV) center magnetic imaging to measure the
properties of individual flakes of CuCrP$_2$S$_6$, a multiferroic van der Waals
magnet known to exhibit weak easy-plane anisotropy in the bulk. We chart the
crossover between in-plane ferromagnetism in thin flakes down to the trilayer,
and the bulk behaviour dominated by a low-field spin-flop transition. Further,
by exploiting the directional dependence of NV center magnetometry, we are able
to observe an instance of a predominantly out-of-plane ferromagetic phase near
zero field, in contradiction with expectation and previous experiments on the
bulk material. We attribute this to the presence of surface anisotropies
arising from the sample preparation process or exposure to the ambient
environment, which is expected to have more general implications for a broader
class of weakly anisotropic van der Waals magnets.
