  Spin Hall magnetoresistance (SMR) has been observed in Pt/NiO/Y3Fe5O12 (YIG)
heterostructures with characteristics very different from those in Pt/YIG. We
show that the SMR in Pt/NiO/YIG strongly correlates with spin conductance, both
sharing very strong temperature dependence due to antiferromagnetic magnons and
spin fluctuation. This phenomenon indicates that spin current generated by spin
Hall effect in the Pt transmits through the insulating NiO and is reflected
from the NiO/YIG interface. Inverted SMR has been observed below a temperature
which increases with the NiO thickness, suggesting spin-flip reflection from
the antiferromagnetic NiO exchange coupled with the YIG.
