Abstract
Bottom IrMn-based spin valves through exposure of part of the CoFe pinned layer to O2 with the structure Ta30/NiFe20/IrMn70/CoFet/oxidation/CoFe(30−t)/Cu20/CoFe30/Ta35 (all thickness in angstroms) (oxidation indicates exposure to different O2 flows) were deposited by dc magnetron sputtering on thermally oxidized Si (111) substrates. Within the range of O2 flows (0.4–2.8 sccm) studied, the value of the magnetoresistance (MR) ratio is seen to be quite low at a relatively large t of >16 Å and a exchange coupling field (Hex) decreases when the O2 exposed CoFe surface is too close to IrMn. Under optimal conditions, a MR ratio of 8.6% with Hex∼275 Oe for the bottom single spin valve and a MR ratio 12.2% with Hex∼268/220 Oe for the dual spin valve are obtained. X-ray reflectivity data show smoother interfaces for the spin valves subjected to O2 exposure. The enhanced MR ratio coupled with the lower interlayer coupling field (Hint), sheet resistance, and magnetic moment of the specular spin valve can be attributed to an enhanced specularity as a result of smoother interfaces after O2 exposure.
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