Exchange enhancement and thermal anneal in Mn76Ir24 bottom-pinned spin valves

Exchange enhancement through thermal anneal in bottom-pinned Mn76Ir24 spin valves is investigated. Samples were fabricated by ion beam deposition (IBD), post-annealed in vacuum (10(-6) Torr) at 270 degreesC for 10 min, then cooled in a 3 kOe applied field. For a bilayer structure, glass/Ta 40 Angstrom /NiFe 30 Angstrom /MnIr 60 Angstrom /CoFe 25 Angstrom /Ta 40 Angstrom, the exchange field (H-ex) reaches 1148 Oe (J(ex) = 0.4 erg/cm(2)) after anneal. X-ray diffraction (XRD) analysis shows strong enhancement of [111] texture upon anneal, while grain size obtained from XRD and transmission electron microscopy for as-deposited and annealed states shows no major change. With increasing MnIr thickness, the exchange field decreases, and blocking temperature (T-b) increases, reaching 295 degreesC for t(MnIr) = 180 Angstrom. Spin valves built with the same exchange bilayer (Ta 20 Angstrom /NiFe 30 Angstrom /MnIr 60 Angstrom /CoFe 25 Angstrom /Cu 22 Angstrom /CoFe 20 Angstrom /NiFe 40 Angstrom /Ta 40 Angstrom) show H-ex = 855 Oe (J(ex) = 0.3 erg/cm(2)) and magnetoresistance (MR) = 7.1%. The incorporation of nano-oxide layers in spin valves increases the MR signal to 11%. No signal degradation is found in these specular structures for anneals up to 310 degreesC. (C) 2001 American Institute of Physics.