Various managed aquifer recharge strategies, such as drywells, are being used in the California Central Valley (CCV) to replenish groundwater resources that have been depleted by over-pumping, especially during droughts. Drywell technology allows recharge water to bypass shallow impermeable layers and possible contaminated soils near the land surface. Understanding water flow in the vadose zone is crucial for assessing the performance of drywells regarding the amount of water that reaches the groundwater table and the fate of solutes. In this study, we demonstrate the applicability of time-lapse electrical resistivity tomography (TL-ERT) for imaging the water flow and subsequent aquifer recharge at a drywell site in the CCV with a thick (67–72 m) vadose zone. Additionally, TL-ERT results were compared to point-scale observations from a collocated monitoring well. To invert our TL-ERT data sets, geostatistical constraints were applied to favor layered models as expected due to the alluvial deposits in the study area. By considering different correlation lengths, an ensemble of resistivity model solutions was generated per time-step instead of a single model solution (as typically performed). Model differences between the mean model of the baseline data set and the models from the subsequent time steps allowed us to image the wetting front development until reaching the regional aquifer, a perched water table, and flush of salts that were otherwise not visible or blurred when using single model solutions from standard deterministic TL-ERT inversion approaches.

Bismuth ferrite has garnered considerable attention as a promising candidate for magnetoelectric spin-orbit coupled logic-in-memory. As model systems, epitaxial BiFeO₃ thin films have typically been deposited at relatively high temperatures (650-800 °C), higher than allowed for direct integration with silicon-CMOS platforms. Here, we circumvent this problem by growing lanthanum-substituted BiFeO₃ at 450 °C (which is reasonably compatible with silicon-CMOS integration) on epitaxial BaPb_0.75Bi_0.25O₃ electrodes. Notwithstanding the large lattice mismatch between the La-BiFeO₃, BaPb_0.75Bi_0.25O₃, and SrTiO₃ (001) substrates, all the layers in the heterostructures are well ordered with a [001] texture. Polarization mapping using atomic resolution STEM imaging and vector mapping established the short-range polarization ordering in the low temperature grown La-BiFeO₃. Current-voltage, pulsed-switching, fatigue, and retention measurements follow the characteristic behavior of high-temperature grown La-BiFeO₃, where SrRuO₃ typically serves as the metallic electrode. These results provide a possible route for realizing epitaxial multiferroics on complex-oxide buffer layers at low temperatures and opens the door for potential silicon-CMOS integration.

Pattern formation in spin systems with continuous-rotational symmetry (CRS) provides a powerful platform to study emergent complex magnetic phases and topological defects in condensed-matter physics. However, its understanding and correlation with unconventional magnetic order along with high-resolution nanoscale imaging are challenging. Here, we employ scanning nitrogen vacancy (NV) magnetometry to unveil the morphogenesis of spin cycloids at both the local and global scales within a single ferroelectric domain of (111)-oriented BiFeO₃, which is a noncollinear antiferromagnet, resulting in formation of a glassy labyrinthine pattern. We find that the domains of locally oriented cycloids are interconnected by an array of topological defects and exhibit isotropic energy landscape predicted by first-principles calculations. We propose that the CRS of spin-cycloid propagation directions within the (111) drives the formation of the labyrinthine pattern and the associated topological defects such as antiferromagnetic skyrmions. Unexpectedly, reversing the as-grown ferroelectric polarization from [[Formula: see text][Formula: see text][Formula: see text]] to [111] produces a noncycloidal NV image contrast which could be attributed to either the emergence of a uniformly magnetized state or a reversal of the cycloid polarity. These findings highlight that (111)-oriented BiFeO₃ is not only important for studying the fascinating subject of pattern formation but could also be utilized as an ideal platform for integrating novel topological defects in the field of antiferromagnetic spintronics.

Antiferromagnets have attracted significant attention in the field of magnonics, as promising candidates for ultralow-energy carriers for information transfer for future computing. The role of crystalline orientation distribution on magnon transport has received very little attention. In multiferroics such as BiFeO₃ the coupling between antiferromagnetic and polar order imposes yet another boundary condition on spin transport. Thus, understanding the fundamentals of spin transport in such systems requires a single domain, a single crystal. We show that through Lanthanum (La) substitution, a single ferroelectric domain can be engineered with a stable, single-variant spin cycloid, controllable by an electric field. The spin transport in such a single domain displays a strong anisotropy, arising from the underlying spin cycloid lattice. Our work shows a pathway to understanding the fundamental origins of magnon transport in such a single domain multiferroic.