  Motivated by experimental work showing enhancement of spin transport between
Yttrium Iron Garnet and Platinum by a thin antiferromagnetic insulator between
them, we consider spin transport through the interface of a non-magnetic metal
and compensated antiferromagnetically ordered insulator and focus on the
significance of the interface itself. The spin transport is carried by
spin-polarized electrons in the metal and by magnons in the insulator. We
compute the spin current in the presence of a spin accumulation in the metal,
cause by the spin Hall effect, and a thermal gradient using Fermi's Golden Rule
in the presence of interfacial disorder. For a perfectly clean interface, the
in-plane momentum is conserved by the electron-magnon scattering events that
govern the spin transport through the interface. We calculate how
disorder-induced broadening of scattering matrix elements with respect to the
in-plane momentum influences the spin current. As a general result, we observe
that for many experimental setups, specifically for high temperatures, one
should expect a rather small effect of interface disorder on the measured spin
current, while for small temperatures there is a significant reduction of a
spin current with increasing disorder.
