  We report the first measurements of effects of large current densities on
current-perpendicular-to-plane magnetoresistance (MR) of magnetic multilayers
containing two antiferromagnetic layers separated by a non-magnetic layer.
These measurements were intended to search for a recently predicted
antiferromagnetic giant magnetoresistance (AGMR) similar to GMR seen in
multilayers containing two ferromagnetic layers separated by a non-magnetic
layer. We report on MR measurements for current injected from point contacts
into sandwiches containing different combinations of layers of F = CoFe and AFM
= FeMn. In addition to: AFM/N/AFM, F/AFM/N/AFM, and F/AFM/N/AFM/F structures,
initial results led us to examine also AFM/F/N/AFM, F/AFM, and single F- and
AFM-layer structures. At low currents, no MR was observed in any samples, and
no MR was observed at any current densities in samples containing only AFMs.
Together, these results indicate that no AGMR is present in these samples. In
samples containing F-layers, high current densities sometimes produced a small
positive MR - largest resistance at high fields. For a given contact
resistance, this MR was usually larger for thicker F-layers, and for a given
current, it was usually larger for larger contact resistances (smaller
contacts). We tentatively attribute this positive MR to suppression at high
currents of spin accumulation induced around and within the F-layers.
