Impact of magnetization and hyperfine field distribution on high magnetoelectric coupling strength in BaTiO₃–BiFeO₃ multilayers

Correlations were established between the hyperfine field distribution around the Fe atoms, the multiferroic properties, and the high magnetoelectric coefficient in BaTiO₃-BiFeO₃ multilayer stacks with variable BiFeO₃ single layer thickness, down to 5 nm. Of key importance in this study was the deposition of ⁵⁷Fe - enriched BiFeO₃, which enhances the sensitivity of conversion electron Mössbauer spectroscopy by orders of magnitude. The magnetoelectric coefficient α_ME reaches a maximum of 60.2 V cm^-1 Oe^-1 at 300 K and at a DC bias field of 2 Tesla for a sample of 15 × (10 nm BaTiO₃-5 nm BiFeO₃) and is one of the highest values reported so far. Interestingly, the highest α_ME is connected to a high asymmetry of the hyperfine field distribution of the multilayer composite samples. The possible mechanisms responsible for the strong magnetoelectric coupling are discussed.