Perpendicular Anisotropy Controlled by Seed and Capping Layers of Heusler-Alloy Films

Abstract

Half-metallic Heusler alloys typically have in-plane magnetic anisotropy, which can be converted to perpendicular by attaching MgO or heavy metal, e.g., Pt, layers as similarly applied for conventional ferromagnets. Recently we have found body-centered cubic (bcc) seed layers, e.g., V and W, to induce perpendicular anisotropy in Heusler-alloy films above, however, they show small giant magnetoresistive (GMR) ratios in spin-valve structures to date. This is partially because of the large resistivity of the seed layer and the nonmagnetic layer in the spinvalve. In this study, we have systematically investigated nonmagnetic overlayers and have found that a Ag layer best maintains the perpendicular anisotropy. The corresponding GMR devices have then been fabricated and characterized, achieving the GMR ratio of ∼0.03% at room temperature. Such bcc seed layers can offer an alternative method for perpendicularly magnetized GMR junctions for applications.