Influence of mesoporous or parasitic BiFeO 3 structural state on the magnetization reversal in multiferroic BiFeO 3/Ni 81Fe 19 polycrystalline bilayers

Coupled ferromagnetic and antiferromagnetic bilayers are an important class of materials that allow manipulating magnetic properties, including the interfacial exchange bias phenomenon. Bismuth ferrite, BiFeO 3, is the most studied single-phase magnetoelectric multiferroic due to its unique ferroelectric and antiferromagnetic orderings well above room temperature. We report on a systematic experimental study regarding the direct correlation between the Bi 2O 3 parasitic phase concentration in the BiFeO 3 and the magnetic properties of the polycrystalline heterostructure BiFeO 3/Ni 81Fe 19 deposited via magnetron sputtering. It was found that the macroscopic exchange field, that arises from exchange bias coupling, is zero for phase-pure BiFeO 3 and increases up to 18 Oe on increasing the concentration of Bi 2O 3. This trend is in agreement with the azimuthal behavior of the magnetization reversal. The structural characterization also indicates that phase-pure BiFeO 3 has a disordered mesoporous structure. The influence of the Bi 2O 3 parasitic phase and mesoporous state, that is known to exist and introduce defects in the polycrystalline bilayers of BiFeO 3/Ni 81Fe 19, on the magnetization reversal and exchange bias coupling is reported for the first time in this study.