  A new class of materials termed topological insulators have been intensively
investigated due to their unique Dirac surface state carrying dissipationless
edge spin currents. Recently, it has been theoretically proposed that the three
dimensional analogue of this type of band structure, the Weyl Semimetal phase,
is materialized in pyrochlore oxides with strong spin-orbit coupling,
accompanied by all-in-all-out spin ordering. Here, we report on the fabrication
and magnetotransport of Eu2Ir2O7 single crystalline thin films. We reveal that
one of the two degenerate all-in-all-out domain structures, which are connected
by time-reversal operation, can be selectively formed by the polarity of the
cooling magnetic field. Once formed, the domain is robust against an oppositely
polarised magnetic field, as evidenced by an unusual odd field dependent term
in the magnetoresistance and an anomalous term in the Hall resistance. Our
findings pave the way for exploring the predicted novel quantum transport
phenomenon at the surfaces/interfaces or magnetic domain walls of pyrochlore
iridates.
