Dynamic and Rotatable Exchange Anisotropy in Fe/KNiF3/FeF2 Trilayers

Results from ferromagnetic resonance experiments carried out on epitaxially grown Fe/KNiF3/FeF2 trilayers are presented. Exchange coupling between the KNiF3, a weak anisotropy antiferromagnet, and the Fe leads to shifts in the resonance field of the ferromagnet. The field shifts can be described by a temperature-dependent exchange anisotropy . depends on the orientation direction of the applied field relative to the magnetic anisotropy axis, and a non-monotonic dependence on KNiF3 thickness. Three thickness regimes appear that correspond to different values of exchange bias in each region. A qualitative understanding of the basis for these three thickness regimes due to spin canting at the interfaces is presented. Our results illustrate a method to tune the value of exchange anisotropy using a combination of different antiferromagnets.