Rotatable anisotropy and mixed interfaces: Exchange bias in Fe/KNiF3

Results from ferromagnetic resonance experiments made on epitaxially grown $\mathrm{Fe}/{\mathrm{KNiF}}_{3}$ bilayers are presented. The bilayers exhibit exchange bias and coercivity previously studied using low-temperature magnetometry. In this paper, results from ferromagnetic resonance (FMR) experiments on the ${\mathrm{FeKNiF}}_{3}$ bilayers are reported. A rotatable anisotropy is identified, and temperature dependence of all anisotropy fields are examined. A possible correlation between the bias field and the rotatable anisotropy is proposed. Linewidths are also studied and possible correlations between coercive fields and FMR linewidths are discussed. A model for the rotatable anisotropy is proposed which ascribes the existence of exchange bias to small uncompensated regions at the interface and rotatable anisotropy to exchange coupling combined with long-range disorder within the antiferromagnet. A possible realization of this mechanism through exchange-coupled grains is discussed in relation to other models for exchange bias in disordered structures.

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