Understanding and Optimizing Magnetoelectric Switching in BiFeO3

Magnetoelectric multiferroics are materials that simultaneously show magnetic and electric orders. Interest in them largely originates from the possibility of affecting one order using the stimulus that usually controls the other, offering great potential for development of multifunctional devices. BiFeO3 is among the most exciting representatives of this family because it displays both orders at room temperature. Moreover, a deterministic reversal of magnetization by an electric field was experimentally observed in BiFeO3 films by J. T. Heron et al. [1]. It has been proposed that this magnetoelectric switching is the result of a peculiar polarization switching process that occurs in two steps: a 109o out-of-plane polarization rotation followed by a 71o in-plane rotation. However, the origin of such two-step polarization reversal is still not well understood, which hampers its optimization (faster switching at a smaller coercive field).<br/><br/>In this work we combine density functional theory (DFT), a phenomenological Landau model and the Landau-Khalatnikov time-evolution equation (LKE) [2] to elucidate the origin of the two-step polarization switching process in BiFeO3. First, we introduce the simplest Landau-like potential for BiFeO3 and ensure that it accurately reproduces the DFT energies and distortion amplitudes for a set of relevant structural polymorphs of BiFeO3 [3]. Then, we extend our model by introducing additional constraints which account for the presence of the substrate and multidomain configuration observed experimentally in BiFeO3 films. We then solve this model using the LKE to investigate the role of the introduced constraints on ferroelectric switching. We are able to reproduce the two-step polarization switching in multidomain system, reveal its physical underpinnings, and identify potential strategies to optimize the switching characteristics.<br/><br/>Work funded by the the Semiconductor Research Corporation and Intel via Contract No. 2018-IN-2865. We also acknowledge the support of the Luxembourg National Research Fund through Grant No. C21/MS/15799044/FERRODYNAMICS and the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement SCALES-897614.<br/><br/>References:<br/><br/>[1] J. T. Heron, J. L. Bosse, Q. He, Y. Gao, M. Trassin, L.Ye, J. D. Clarkson, C.Wang, Jian Liu, S. Salahuddin, D. C. Ralph, D. G. Schlom, J. Íñiguez, B. D. Huey and R. Ramesh, Deterministic switching of ferromagnetism at room temperature using an electric field. Nature 516, 370 (2014).<br/><br/>[2] A. Umantsev, Field theoretic method in phase transformations. Springer, New York (2012).<br/><br/>[3] N. S. Fedorova, D. E. Nikonov, H. Li, I. A. Young, and J. Íñiguez, First-principles Landau-like potential for BiFeO3 and related materials. Phys. Rev. B 106, 165122 (2022).