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The dependence of the exchange bias field and coercivity enhancement on ferromagnetic (FM) and antiferromagnetic (AF) layer thickness in exchange biased bilayers has been systematically investigated in CoFe/FeMn and CoFe/PdMn bilayers for digital encoding applications in biotechnology. A magnetic multilayer structure can be used as a digitally encoded tag if each (bi)layer has two magnetic states, positive and negative saturation, available at remanence and if each layer can be uniquely identified by its coercivity. We will demonstrate that by adjusting the AF and FM layer thickness in an AF/FM bilayer, both the bias field and the coercivity of the bilayer can be controlled. By contrasting CoFe/FeMn bilayers with CoFe/PdMn bilayers, it becomes apparent that the relative magnitudes of the coercivity enhancement and bias field depend on the particular AF material, although the qualitative behavior remains unchanged. In order to create a multilayer that can retain one of many magnetic states at remanence, a large coercivity enhancement but absent or small bias field are preferred. Analysis of the bilayers suggest that PdMn is a better choice of AF layer for this purpose and results on some multilayer films are shown which validate this claim.

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