Exchange bias in antiferromagnetic-ferromagnetic-antiferromagnetic structures with out-of-plane magnetization

Exchange bias effects are investigated in antiferromagnetic- (AF₁-) ferromagnetic- (F-) antiferromagnetic (AF₂) structures, where the F consists of a [Pt∕Co] multilayer with perpendicular anisotropy and the two AF layers are composed of IrMn. The AF₁ and AF₂ thicknesses are varied so that the two IrMn layers exhibit different blocking temperatures. After field cooling, enhancements of the coercivity HC and exchange bias field HE are observed in the AF₁-F-AF₂ structures with respect to the two subsystems with a single AF layer (i.e., AF₁-F and F-AF₂). For all systems, the magnitude and sign of HE can be subsequently tailored by field cooling processes under fields of different sign while HC remains constant. The net effect of having two AF-F interfaces is roughly the sum of each individual interface contribution.