  We prepare the high quality epitaxial
MgO(001)[100]/Pt(001)[100]/NiO(001)[100]/FeNi/SiO2 films to investigate the
spin transport in the NiO antiferromagnetic insulator. The ferromagnetic
resonance measurements of the FeNi under a spin current injection from the Pt
by the spin Hall effect revealed the change of the ferromagnetic resonance
linewidth depending on the amount of the spin current injection. The results
can be interpreted that there is an angular momentum transfer through the NiO.
A high efficient angular momentum transfer we observed in the epitaxial NiO can
be attributed to the well-defined orientation of the antiferromagnetic moments
and the spin quantization axis of the injected spin current.
