Enhanced blocking temperature in (Pt/Co)3/IrMn/Co and (Pd/Co)3/IrMn/Co trilayers with ultrathin IrMn layer

IrMn blocking temperature (T-B) is compared between IrMn/Co bilayers and (Pt/Co)(3)/IrMn/Co and (Pd/Co)(3)/IrMn/Co trilayers for different IrMn thicknesses. Exchange bias field (H-ex) is measured from 5 to 400 K. Trilayers show a more concave thermal decrease of H-ex(T) compared to bilayers and, for thin IrMn layers, larger T-B and sharper peak of coercive field H-c around T-B. This H-ex(T) behaviour presents improved characteristics for thermally assisted-MRAM (TA-MRAM) applications, with large H-ex/H-c ratio. Two physical explanations are proposed: an indirect IrMn intergrain coupling through the (Pt(Pd)/Co)(3) layer and a reduction of IrMn/Co interfacial coupling due to out-of-plane canting of the IrMn spins.