  A topological insulator is a state of matter which does not break any
symmetry and is characterized by topological invariants, the integer
expectation values of non-local operators. Antiferromagnetism on the other hand
is a broken symmetry state in which the translation symmetry is reduced and
time reversal symmetry is broken. Can these two phenomena coexist in the same
material? A proposal by Mong {\it et al.}\cite{Mong2010} asserts that the
answer is yes. Moreover, it is theoretically possible that the onset of
antiferromagnetism enables the non-trivial topology since it may create
spin-orbit coupling effects which are absent in the non-magnetic phase. The
current work examines a real system, half-Heusler GdBiPt, as a candidate for
topological anti ferromagnetism. We find that the magnetic moments of the
gadolinium atoms form ferromagnetic sheets which are stacked
antiferromagnetically along the body diagonal. This magnetic structure may
induce spin orbit coupling on band electrons as they hop perpendicular to the
ferromagnetic sheets.
