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

Abstract

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 °C for 10 min, then cooled in a 3 kOe applied field. For a bilayer structure, glass/Ta 40 Å/NiFe 30 Å/MnIr 60 Å/CoFe 25 Å/Ta 40 Å, the exchange field (Hex) reaches 1148 Oe (Jex=0.4 erg/cm2) 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 (Tb) increases, reaching 295 °C for tMnIr=180 Å. Spin valves built with the same exchange bilayer (Ta 20 Å/NiFe 30 Å/MnIr 60 Å/CoFe 25 Å/Cu 22 Å/CoFe 20 Å/NiFe 40 Å/Ta 40 Å) show Hex=855 Oe (Jex=0.3 erg/cm2) 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 °C.