  The interplay between electronic interactions and strong spin-orbit coupling
is expected to create a plethora of fascinating correlated topological states
of quantum matter. Of particular interest are magnetic Weyl semimetals
originally proposed in the pyrochlore iridates, which are only expected to
reveal their topological nature in thin film form. To date, however, direct
experimental demonstrations of these exotic phases remain elusive, due to the
lack of usable single crystals and the insufficient quality of available films.
Here, we report on the discovery of the long-sought magnetic Weyl semi-metallic
phase in (111)-oriented Eu$_2$Ir$_2$O$_7$ high-quality epitaxial thin films.
The topological magnetic state shows an intrinsic anomalous Hall effect with
colossal coercivity but vanishing net magnetization, which emerges below the
onset of a peculiar magnetic phase with all-in-all-out antiferromagnetic
ordering. The observed anomalous Hall conductivity arises from the non-zero
Berry curvature emanated by Weyl node pairs near the Fermi level that act as
sources and sinks of Berry flux, activated by broken cubic crystal symmetry at
the top and bottom terminations of the thin film.
