  The topological transition in the strongly correlated half-metallic
ferromagnetic compound Co$_3$Sn$_2$S$_2$ from Weyl semimetal (including chiral
massless fermions) to a non-magnetic state is treated. This transition goes
with a change in topological invariant, and is accompanied by a non-topological
transition from saturated ferromagnetic to paramagnetic state, the minority
Fermi surface being transformed from ghost (hidden) to real. A corresponding
description is given in terms of slave fermion representation for the effective
narrow-band Hubbard model. The system Co$_3$Sn$_2$S$_2$ provides a bright
example of coexistence of non-trivial topology and strong low-dimensional
ferromagnetism. A comparison is performed with other compounds where
frustrations result in formation of a correlated paramagnetic state.
