Enhancement of exchange bias in Mn-Ir/Co-Fe based spin valves with an ultrathin Cu underlayer and in situ Mn-Ir surface modification

Enhancement of exchange bias induced at the interface of the antiferromagne tic (AF)/ferromagnetic (F) layers was studied using the bottom "spin-valve films" (SVs) with the Mn-Ir/Co-Fe exchange coupled films. Exchange bias inc reased using an ultrathin Cu underlayer. Meanwhile, both exchange bias fiel d, H-ex, and blocking temperature, T-B, increased intensively by heating sp ecimens after depositing Mn-Ir film in a high vacuum. These two enhancement effects worked in an additive. As a result, an unidirectional anisotropy c onstant, J(K), of 0.39 erg/cm(2) (H-ex of 1.3 kOe) and T-B of similar to 32 5 degreesC were obtained for the bottom SVs with a total thickness of 233 A ngstrom including an AF layer of 68 Angstrom Mn74Ir26 and a pinned layer of 20 Angstrom Co90Fe10, where the SVs were field annealed at 320 degreesC. A microstructural analysis using x-ray diffraction revealed that H-ex did no t depend on the diffraction intensity from Mn-Ir (111) for the SVs with var ious underlayers, and no remarkable changes occurred in the microstructure of the SVs with the heating treatment in a vacuum. Therefore, the enhanceme nt effects might result from some changes in the microstructure and/or the morphology of the interface of AF/F layers. (C) 2001 American Institute of Physics.