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1. Ferroelectric Domain Wall Memristor

   https://doi.org/10.1002/adfm.202000109  

   McConville, James_P_V; Lu, Haidong; Wang, Bo; Tan, Yueze; Cochard, Charlotte; Conroy, Michele; Moore, Kalani; Harvey, Alan; Bangert, Ursel; Chen, Long‐Qing; et al (May 2020, Advanced Functional Materials)

   Abstract 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. 

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2. Interplay between Point and Extended Defects and Their Effects on Jerky Domain-Wall Motion in Ferroelectric Thin Films

   https://doi.org/10.1103/PhysRevLett.133.106801  

   Bulanadi, Ralph; Cordero-Edwards, Kumara; Tückmantel, Philippe; Saremi, Sahar; Morpurgo, Giacomo; Zhang, Qi; Martin, Lane W; Nagarajan, Valanoor; Paruch, Patrycja (September 2024, Physical Review Letters)

   Defects have a significant influence on the polarization and electromechanical properties of ferroelectric materials. Statistically, they can be seen as random pinning centers acting on an elastic manifold, slowing domain-wall propagation and raising the energy required to switch polarization. Here we show that the “dressing” of defects can lead to unprecedented control of domain-wall dynamics. We engineer defects of two different dimensionalities in ferroelectric oxide thin films—point defects externally induced via ${\mathrm{He}}^{2+}$bombardment, and extended quasi-one-dimensional $a$domains formed in response to internal strains. The $a$domains act as extended strong pinning sites (as expected) imposing highly localized directional constraints. Surprisingly, the induced point defects in the ${\mathrm{He}}^{2+}$bombarded samples orient and align to impose further directional pinning, screening the effect of $a$domains. This defect interplay produces more uniform and predictable domain-wall dynamics. Such engineered interactions between defects are crucial for advancements in ferroelectric devices. Published by the American Physical Society2024 

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3. Electrical Tunability of Domain Wall Conductivity in LiNbO ₃ Thin Films

   https://doi.org/10.1002/adma.201902890  

   Lu, Haidong; Tan, Yueze; McConville, James_P_V; Ahmadi, Zahra; Wang, Bo; Conroy, Michele; Moore, Kalani; Bangert, Ursel; Shield, Jeffrey_E; Chen, Long‐Qing; et al (October 2019, Advanced Materials)

   Abstract Domain wall nanoelectronics is a rapidly evolving field, which explores the diverse electronic properties of the ferroelectric domain walls for application in low‐dimensional electronic systems. One of the most prominent features of the ferroelectric domain walls is their electrical conductivity. Here, using a combination of scanning probe and scanning transmission electron microscopy, the mechanism of the tunable conducting behavior of the domain walls in the sub‐micrometer thick films of the technologically important ferroelectric LiNbO₃is explored. It is found that the electric bias generates stable domains with strongly inclined domain boundaries with the inclination angle reaching 20° with respect to the polar axis. The head‐to‐head domain boundaries exhibit high conductance, which can be modulated by application of the sub‐coercive voltage. Electron microscopy visualization of the electrically written domains and piezoresponse force microscopy imaging of the very same domains reveals that the gradual and reversible transition between the conducting and insulating states of the domain walls results from the electrically induced wall bending near the sample surface. The observed modulation of the wall conductance is corroborated by the phase‐field modeling. The results open a possibility for exploiting the conducting domain walls as the electrically controllable functional elements in the multilevel logic nanoelectronics devices. 

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4. Domain-wall magnetoelectric coupling in multiferroic hexagonal YbFeO3 films

   https://doi.org/10.1038/s41598-023-28365-x  

   Li, Xin; Yun, Yu; Thind, Arashdeep Singh; Yin, Yuewei; Li, Qiang; Wang, Wenbin; N’Diaye, Alpha T.; Mellinger, Corbyn; Jiang, Xuanyuan; Mishra, Rohan; et al (January 2023, Scientific Reports)

   Abstract Electrical modulation of magnetic states in single-phase multiferroic materials, using domain-wall magnetoelectric (ME) coupling, can be enhanced substantially by controlling the population density of the ferroelectric (FE) domain walls during polarization switching. In this work, we investigate the domain-wall ME coupling in multiferroic h-YbFeO₃thin films, in which the FE domain walls induce clamped antiferromagnetic (AFM) domain walls with reduced magnetization magnitude. Simulation according to the phenomenological theory indicates that the domain-wall ME effect is dramatically enhanced when the separation between the FE domain walls shrinks below the characteristic width of the clamped AFM domain walls during the ferroelectric switching. Experimentally, we show that while the magnetization magnitude remains same for both the positive and the negative saturation polarization states, there is evidence of magnetization reduction at the coercive voltages. These results suggest that the domain-wall ME effect is viable for electrical control of magnetization. 

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5. Active subspace analysis and uncertainty quantification for a polydomain ferroelectric phase-field model

   https://doi.org/10.1177/1045389X19853636  

   Leon, Lider_S; Miles, Paul_R; Smith, Ralph_C; Oates, William_S (July 2019, Journal of Intelligent Material Systems and Structures)

   We perform parameter subset selection and uncertainty analysis for phase-field models that are applied to the ferroelectric material lead titanate. A motivating objective is to determine which parameters are influential in the sense that their uncertainties directly affect the uncertainty in the model response, and fix noninfluential parameters at nominal values for subsequent uncertainty propagation. We employ Bayesian inference to quantify the uncertainties of gradient exchange parameters governing 180° and 90° tetragonal phase domain wall energies. The uncertainties of influential parameters determined by parameter subset selection are then propagated through the models to obtain credible intervals when estimating energy densities quantifying polarization and strain across domain walls. The results illustrate various properties of Landau and electromechanical coupling parameters and their influence on domain wall interactions. We employ energy statistics, which quantify distances between statistical observations, to compare credible intervals constructed using a complete set of parameters against an influential subset of parameters. These intervals are obtained from the uncertainty propagation of the model input parameters on the domain wall energy densities. The investigation provides critical insight into the development of parameter subset selection, uncertainty quantification, and propagation methodologies for material modeling domain wall structure evolution, informed by density functional theory simulations. 

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