Enhanced blocking temperature in (Pt/Co)$_3$/IrMn/Co and (Pd/Co)$_3$/IrMn/Co trilayers with ultrathin IrMn layer
Résumé
rMn 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 Hc around $TB$. 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.