Nonlinear and hysteretic exchange bias in antiferromagnetically coupled ferromagnetic bilayers

We report observations of nonlinear and hysteretic exchange bias in antiferromagnetically coupled hard/soft ferromagnetic bilayers. In such systems, the hard ferromagnetic layer acts as a tunable biasing layer replacing the antiferromagnet used in conventional exchange bias structures. It is shown that the reported behavior is due to the reciprocity of the exchange bias effect in conjunction with the presence of locally varying interfacial exchange which causes a preferential magnetization of the weakly exchange-coupled tuning regions during the exchange bias setting stage.