Local probing of electric field-induced oxidation of ferromagnetic/ferroelectric interfaces

In multiferroic materials, the coupling between ferroic order parameters like ferromagnetism (FM) and ferroelectricity (FE) (called magnetoelectric (ME) coupling) attracts significant attention. In our work we couple the FM... [ view full abstract ]

In multiferroic materials, the coupling between ferroic order parameters like ferromagnetism (FM) and ferroelectricity (FE) (called magnetoelectric (ME) coupling) attracts significant attention. In our work we couple the FM and FE materials via an interface in a multilayer structure with the aim of studying in detail the magnetic spin structure at the interface. We have studied the evolution of the interface of Fe/(LNO, BTO) systems as function of the applied electric field using the isotope sensitivity of Mössbauer spectroscopy and nuclear resonant scattering (NRS) of synchrotron radiation on samples with a 1 nm ⁵⁷Fe probe layer at the interface. The results show the formation of a thin magnetically dead layer at the interface between the metal and the Fe oxide due to ion transport across the interface. Based on our results we propose a model [1] for the effect of an electric field on the metal/FE oxide interface and validated it with Mössbauer spectroscopy results. During the growth of a metal on top of a FE oxide, electron transport occurs across the interface due to the work function difference between the metal and the oxide (with high dielectric constant), which leads to the formation of a built-in electric field at the interface. Depending on the direction of the built-in field, the direction of the applied electric field either favors the ion transport across the interface or opposes it until the external field overcomes the built-in field (after applying electric field above a critical value). With recent NRS results, we have identified the values of the critical field for both Fe/BTO and Fe/LNO systems. These findings are not only applicable to Fe/(LNO,BTO) interfaces but also improve the understanding of metal/FE oxide interfaces in general.

References

• Manisha Bisht et al., Advanced Materials Interfaces 3, 1500433 (2016)