A domain wall‐enabled memristor is created, in thin film lithium niobate capacitors, which shows up to twelve orders of magnitude variation in resistance. Such dramatic changes are caused by the injection of strongly inclined conducting ferroelectric domain walls, which provide conduits for current flow between electrodes. Varying the magnitude of the applied electric‐field pulse, used to induce switching, alters the extent to which polarization reversal occurs; this systematically changes the density of the injected conducting domain walls in the ferroelectric layer and hence the resistivity of the capacitor structure as a whole. Hundreds of distinct conductance states can be produced, with current maxima achieved around the coercive voltage, where domain wall density is greatest, and minima associated with the almost fully switched ferroelectric (few domain walls). Significantly, this “domain wall memristor” demonstrates a plasticity effect: when a succession of voltage pulses of constant magnitude is applied, the resistance changes. Resistance plasticity opens the way for the domain wall memristor to be considered for artificial synapse applications in neuromorphic circuits.

Domain wall nanoelectronics is a rapidly evolving field, which explores the diverse electronic properties of the ferroelectric domain walls for application in lowdimensional electronic systems. One of the most prominent features of the ferroelectric

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Multiferroic topologies are an emerging solution for future low-power magnetic nanoelectronics due to their combined tuneable functionality and mobility. Here, we show that in addition to being magnetoelectric multiferroic at room temperature, thin-film Aurivillius phase Bi 6 Ti x Fe y Mn z O 18 is an ideal material platform for both domain wall and vortex topology-based nanoelectronic devices. Utilizing atomic-resolution electron microscopy, we reveal the presence and structure of 180°-type charged head-to-head and tail-to-tail domain walls passing throughout the thin film. Theoretical calculations confirm the subunit cell cation site preference and charged domain wall energetics for Bi 6 Ti x Fe y Mn z O 18 . Finally, we show that polar vortex-type topologies also form at out-of-phase boundaries of stacking faults when internal strain and electrostatic energy gradients are altered. This study could pave the way for controlled polar vortex topology formation via strain engineering in other multiferroic thin films. Moreover, these results confirm that the subunit cell topological features play an important role in controlling the charge and spin state of Aurivillius phase films and other multiferroic heterostructures.

At lower temperatures (≈255 K [1] ), however, the original high-symmetry para electric-orthorhombic state is restored. Symmetry associated with this re-entrant phase transition has unusually, therefore, increased on cooling. Some observations show that this generates a local dip in the heat capacity, [1,2] stalling entropy reduction on decreasing temperature. [1] Strange symmetry transformations also occur in flux-grown barium titanate crystals, where highly ordered "Forsbergh Patterns" can first appear and then subsequently disappear, as temperature is monotonically varied. [3,4] Most recently, heating has been seen to cause high symmetry labyrinthine ferroelectric domain patterns to give way to lower symmetry stripe arrays: an effect classified as an "inverse transition". [5] Clearly, symmetry changes can therefore occasionally occur in the opposite sense to that normally seen. While fundamental thermodynamic laws are not broken, such cases are unusual, arresting, and worthy of note. [6]