Accessing intermediate ferroelectric switching regimes with time-resolved transmission electron microscopy

BiFeO₃ (BFO) is one of the most widely studied magneto-electric multiferroics. The magneto-electric coupling in BiFeO₃, which allows for the control of the ferroelectric and magnetic domain structures via applied electric fields, can be used to incorporate BiFeO₃ into novel spintronics devices and sensors. Before BiFeO₃ can be integrated into such devices, however, a better understanding of the dynamics of ferroelectric switching, particularly in the vicinity of extended defects, is needed. We use in situ transmission electron microscopy (TEM) to investigate the response of ferroelectric domains within BiFeO₃ thin films to applied electric fields at high temporal and spatial resolution. This technique is well suited to imaging the observed intermediate ferroelectric switching regimes, which occur on a time- and length-scale that are too fine to study via conventional scanning-probe techniques. Additionally, the spatial resolution of transmission electron microscopy allows for the direct study of the dynamics of domain nucleation and propagation in the presence of structural defects. In this article, we show how this high resolution technique captures transient ferroelectric structures forming during biasing, and how defects can both pin domains and act as a nucleation source. The observation of continuing domain coalescence over a range of times qualitatively agrees with the nucleation-limited-switching model proposed by Tagantsev et al. We demonstrate that our in situ transmission electron microscopy technique is well-suited to studying the dynamics of ferroelectric domains in BiFeO₃ and other ferroelectric materials. These biasing experiments provide a real-time view of the complex dynamics of domain switching and complement scanning-probe techniques.