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 spin-valve. 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.
Highlights
INTRODUCTIONH EUSLER alloys have been investigated intensively due to their half-metallicity at room temperature, which is considered an ideal spin source for spintronic devices [1]–[3]
H EUSLER alloys have been investigated intensively due to their half-metallicity at room temperature, which is considered an ideal spin source for spintronic devices [1]–[3].The alloys can exhibit other magnetism by controlling the number of valence band electrons in the alloys and the associated magnetic interactions, achieving antiferromagnetism [4], ferrimagnetism [5], topological insulator [6], and spin gapless semiconductor [7]
We systematically investigate the effect of seed and capping layers on Co-based Heusler-alloy films, which can be used as a nonmagnetic layer in a giant magnetoresistive (GMR) junction
Summary
H EUSLER alloys have been investigated intensively due to their half-metallicity at room temperature, which is considered an ideal spin source for spintronic devices [1]–[3]. For these device applications, a film form of Heusler alloys has some obstacles, including their large crystallization energy, atomic disordering in the film and interfaces, and magnetic isotropy due to their cubic unit cells [11]. To date significant efforts have been made to induce perpendicular magnetic anisotropy (PMA) in a Heusler-alloy film by attaching a perpendicularly magnetized ferromagnet [13] or MgO layer [14] The latter structures can be useful for TMR junctions [15]. Ag spacers in a GMR junction show consistent magnetization reversal and small interfacial mixing, which is ideal for the device applications, achieving a GMR ratio of ∼0.03% at room temperature
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