  Co3Sn2S2, a ferromagnetic Weyl semi-metal with Co atoms on a kagome lattice,
has generated much recent attention. Experiments have identified a temperature
scale below the Curie temperature. Here, we find that this magnet keeps a
memory, when not exposed to a magnetic field sufficiently large to erase it. We
identify the driver of this memory effect as a small secondary population of
spins, whose coercive field is significantly larger than that of the majority
spins. The shape of the magnetization hysteresis curve has a threshold magnetic
field set by the demagnetizing factor. These two field scales set the hitherto
unidentified temperature scale, which is not a thermodynamic phase transition,
but a crossing point between meta-stable boundaries. Global magnetization is
well defined, even when it is non-uniform, but drastic variations in local
magnetization point to a coarse energy landscape, with the thermodynamic limit
not achieved at micrometer length scales.
