Antiferromagnet thickness dependence of top and bottom giant magnetoresistance spin valve multilayers

We investigated the dependence of magnetic properties and microstructure on Mn-Ir-Pt antiferromagnet(AFM) thickness in a top and bottom spin valve (SV). After annealing, the critical thickness (t(cr)), which exhibited a maximum exchange coupling field (H-ex), was 50 Angstrom in a top and bottom SVs. However, both SVs showed a different behavior in the dependence of a H,x on Mn-Ir-Pt thickness (t(Mn-Ir-Pt)). The rapid decrease of H-ex in a bottom SV compared with a top SV comes from a large lattice mismatch at the interface of a pinned layer (PL)/Mn-Ir-Pt, which may lead to grow the randomly oriented pinned layer (PL). From X-ray diffraction analysis, We confirmed that the decrease of (111) texture in a PL correlated with the deterioration of thermal stability at a lower temperature than 100 degreesC. All SVs with thicker Mn-Ir-Pt of t(Mn-Ir-Pt) greater than or equal to 90 Angstrom showed a blocking temperature of over 230 degreesC. From a transmission electron microscopy study, a top SV has a highly oriented (111) plane in an all layers. But, the bottom SV shows a poor (111) texture in a PL as the increase of t(Mn-Ir-Pt).