Giant Magnetoresistance of Fe/Ag Multilayer Films with Ultrathin Fe Layers

A giant magnetoresistive effect in as-deposited Fe/Ag multilayer films with ultrathin Fe layers has been observed. The magnetoresistance in this system is presented first as a function of Fe layer thickness t_Fe. The sample with Fe layer thickness of 4Å exhibits a magnetoresistance ratio as large as 14.3% at 4.2K. The magnetoresistance ratio decreases approximately an order of magnitude with increasing t_Fe from 4 to 10Å and then changes slightly with further increasing t_Fe. From the hysteresis loop measurement, it is found that the interlayer coupling changes from antiferromagnetic to ferromagnetic with increasing t_Fe. The feature of material at the interface might be responsible for all these findings.