CPP-GMR With Current Screen Layer Using Various Co-Fe Compositions

We investigated current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) with current screen layer of various Co-Fe compositions. The resistance-area product (RA) and the change in the resistance-area product (DeltaRA) increased with increasing Fe compositions in the current screen layer up to 25 at.%. However, they were very low at Fe compositions above 50 at.%. It seemed that the boundaries of the RA and Delta RA dependences on Co-Fe composition were similar to that of the Co-Fe composition between fcc and bcc structures. Based on transmission electron microscopic observations, the current screen layer composed of Co₉₀Fe₁₀ was formed uniformly, and it had an epitaxially crystalline structure. On the other hand, the current screen layer composed of Co₅₀Fe ₅₀ was formed with a large degree of roughness, and it had a complicated crystalline structure. This suggests that a uniform current screen layer with an epitaxially crystalline structure is important to enhance the MR ratio for CPP-GMR