Nanoscale Imaging of Current Flow Within Ferroelectric Domain Walls with a Single-Spin Magnetometer

While C-AFM has been a valuable tool in characterizing conductivity variations in ferroelectric materials, it is increasingly evident that its limitations hinder a complete understanding of the intrinsic nature of conductive domain walls. Due to its invasive nature, the system will always be perturbed to force current flow along predetermined pathways. Although C-AFM captures a qualitative understanding of the conductivity along that path, it doesn’t provide a complete and quantitative characterization of the true pathways electrons will ideally choose throughout the sample. For electrons to flow unperturbed throughout the system, a different way of probing the system will be required, one which does not lead to interactions with the system's electric fields. If achieved, more fundamental insights could be developed into electronic transport along ferroelectric domains, while producing a platform for additional novel experiments where the invasive nature of C-AFM limits access to the physical phenomena.

Here, we demonstrate the use of a scanning nitrogen vacancy (NV) magnetometer to provide non-invasive, high-resolution images of the current flow by measuring the emanating Oersted field of conducting domain walls. This technique uses a single NV center at room temperature attached to a tuning-fork-based AFM to bring the NV within close proximity to a sample surface (<50nm) to capture minute (<µT/Hz^1/2) changes in the magnetic fields associated with the current flow through ferroelectric domain walls. The NV’s ability to capture complete vector magnetic fields allows for the captured magnetic map to provide information about the current density through the use of inverse propagation procedures, from which assumptions can be made about the transport dynamics and domain wall morphologies.

In this work, we provide evidence for the capabilities of NV magnetometers to measure non-invasively the current flowing within ferroelectric systems. We demonstrate that quantitative values for the current density can be taken, along with discussion that when the process is extended further estimates for domain wall thickness can be obtained. These results demonstrate the capability of NV magnetometers to study a range of highly conductive ferroelectric systems, paving the way for deeper insights into their electronic transport properties and potential applications in advanced electronic devices and emerging technologies.