  Effectively manipulating magnetism in ferromagnet (FM) thin film
nanostructures with an in-plane current has become feasible since the
determination of a 'giant' spin Hall effect (SHE) in certain heavy metal
(HM)/FM system. Recently, both theoretical and experimental reports indicate
that the non-collinear and collinear metallic antiferromagnet (AF) materials
can have both a large anomalous Hall effect (AHE) and a strong SHE. Here we
report a systematic study of the SHE in PtMn with several PtMn/FM systems. By
using interface engineering to reduce the 'spin memory loss' we obtain a spin
torque efficiency as large as 0.24. This is more than twice the previously
reported spin torque efficiency for PtMn. We also find that the apparent spin
diffusion length in PtMn is surprisingly long (about 2.3nm).
