Point-contact search for antiferromagnetic giant magnetoresistance

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.