  We consider an antiferromagnetic insulator that is in contact with a metal.
Spin accumulation in the metal can induce spin-transfer torques on the
staggered field and on the magnetization in the antiferromagnet. These torques
relate to spin pumping: the emission of spin currents into the metal by a
precessing antiferromagnet. We investigate how the various components of the
spin-transfer torque are affected by spin-independent disorder and spin-flip
scattering in the metal. Spin-conserving disorder reduces the coupling between
the spins in the antiferromagnet and the itinerant spins in the metal in a
manner similar to Ohm's law. Spin-flip scattering leads to spin-memory loss
with a reduced spin-transfer torque. We discuss the concept of a staggered spin
current and argue that it is not a conserved quantity. Away from the interface,
the staggered spin current varies around a zero mean in an irregular manner. A
network model explains the rapid decay of the staggered spin current.
