Abstract
Enhancement of giant magnetoresistance properties of single (bottom) and dual IrMn-based spin valves through exposure of part of the CoFe pinned layer to O2 is reported. Under optimal conditions, a ΔR/R of 10.4% [Hua=460 Oe, Hf=5.1 Oe, and Hc=4.7 Oe for a free and pinned layer thickness (permalloy equivalent) of 50 Å each] for an ion beam sputtered single spin valve, and a ΔR/R of as high as 20.5% for a magnetron sputtered dual spin valve having a 30 Å thick CoFe free layer are observed, compared to a value of 6.5% and 10.6% for the corresponding spin valve without O2 exposure, respectively. Transmission electron microscopy results reveal the presence of a thin (10 Å) crystalline oxygen-containing layer near the IrMn–CoFe pinned layer interface as a result of O2 exposure. X-ray reflectivity data show smoother interfaces for the spin valves subjected to O2 exposure, consistent with the lower Hf and smaller sheet resistance observed for these samples. The enhanced ΔR/R thus can be attributed to improved growth after O2 exposure.
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