  Interest in creating magnetic metamaterials has led to methods for growing
superstructures of magnetic nanoparticles. Mesoscopic crystals of maghemite
($\gamma\text{-Fe}_2\text{O}_3$) nanoparticles can be arranged into highly
ordered body-centered tetragonal lattices of up to a few micrometers. Although
measurements on disordered ensembles have been carried out, determining the
magnetic properties of individual mesoscopic crystals is challenging due to
their small total magnetic moment. Here, we overcome these challenges by
utilizing sensitive dynamic cantilever magnetometry to study individual
micrometer-sized $\gamma\text{-Fe}_2\text{O}_3$ mesocrystals. These
measurements reveal an unambiguous cubic anisotropy, resulting from the
crystalline anisotropy of the constituent maghemite nanoparticles and their
alignment within the mesoscopic lattice. The signatures of anisotropy and its
orgins come to light because we combine the self-assembly of highly ordered
mesocrystals with the ability to resolve their individual magnetism. This
combination is promising for future studies of the magnetic anisotropy of other
nanoparticles, which are too small to investigate individually.
