  Inducing magnetism onto a topological crystalline insulator (TCI) has been
predicted to result in several novel quantum electromagnetic effects. This is a
consequence of the highly strain-sensitive band topology of such
symmetry-protected systems. We thus show that placing the TCI surface of SnTe
in proximity to EuS, a ferromagnetic insulator, induces magnetism at the
interface between SnTe and EuS and thus breaks time-reversal-symmetry in the
TCI. Magnetotransport experiments on SnTe-EuS-SnTe trilayer devices reveal a
hysteretic lowering of the resistance at the TCI surface that coincides with an
increase in the density of magnetic domain walls. This additional conduction
could be a signature of topologically-protected surface states within domain
walls. Additionally, a hysteretic anomalous Hall effect reveals that the usual
in-plane magnetic moment of the EuS layer is canted towards a perpendicular
direction at the interface. These results are evidence of induced magnetism at
the SnTe-EuS interfaces resulting in broken time-reversal symmetry in the TCI.
