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.
MacDonald and co-workers recently predicted that high current densities could affect the magnetic order of antiferromagnetic (AFM) multilayers, in ways similar to those that occur in ferromagnetic (F) multilayers, and that changes in AFM magnetic ord
er can produce an antiferromagnetic Giant Magnetoresistance (AGMR). Four groups have now studied current-driven effects on exchange bias at F/AFM interfaces. In this paper, we first briefly review the main predictions by MacDonald and co-workers, and then the results of experiments on exchange bias that these predictions stimulated.
