Driving mechanism of exchange bias and magnetic anisotropy in multiferroic polycrystalline BiFeO3/permalloy bilayers

Magnetization reversal processes of Permalloy exchange coupled with thin polycrystalline antiferromagnetic multiferroic BiFeO3 films were investigated. The BiFeO3 critical thickness and the interfacial exchange energy are comparable with similar epitaxially grown systems. However, the coercive field dependence on multiferroic thickness presents an atypical behaviour. This system shows induced unidirectional, uniaxial, and biquadratic-like behaviour with misalignment of magnetic easy axis with respect to pinning field direction. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4763480]