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Abstract 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.

Abstract Stabilization of topological spin textures in layered magnets has the potential to drive the development of advanced low-dimensional spintronics devices. However, achieving reliable and flexible manipulation of the topological spin textures beyond skyrmion in a two-dimensional magnet system remains challenging. Here, we demonstrate the introduction of magnetic iron atoms between the van der Waals gap of a layered magnet, Fe3GaTe2, to modify local anisotropic magnetic interactions. Consequently, we present direct observations of the order-disorder skyrmion lattices transition. In addition, non-trivial topological solitons, such as skyrmioniums and skyrmion bags, are realized at room temperature. Our work highlights the influence of random spin control of non-trivial topological spin textures.

Abstract Bismuth ferrite (BiFeO3) is a multiferroic material that exhibits both ferroelectricity and canted antiferromagnetism at room temperature, making it a unique candidate in the development of electric-field controllable magnetic devices. The magnetic moments in BiFeO3 are arranged into a spin cycloid, resulting in unique magnetic properties which are tied to the ferroelectric order. Previous understanding of this coupling has relied on average, mesoscale measurements. Using nitrogen vacancy-based diamond magnetometry, we observe the magnetic spin cycloid structure of BiFeO3 in real space. This structure is magnetoelectrically coupled through symmetry to the ferroelectric polarization and this relationship is maintained through electric field switching. Through a combination of in-plane and out-of-plane electrical switching, coupled with ab initio studies, we have discovered that the epitaxy from the substrate imposes a magnetoelastic anisotropy on the spin cycloid, which establishes preferred cycloid propagation directions. The energy landscape of the cycloid is shaped by both the ferroelectric degree of freedom and strain-induced anisotropy, restricting the spin spiral propagation vector to changes to specific switching events.

Abstract As CMOS technologies face challenges in dimensional and voltage scaling, the demand for novel logic devices has never been greater, with spin-based devices offering scaling potential, at the cost of significantly high switching energies. Alternatively, magnetoelectric materials are predicted to enable low-power magnetization control, a solution with limited device-level results. Here, we demonstrate voltage-based magnetization switching and reading in nanodevices at room temperature, enabled by exchange coupling between multiferroic BiFeO3 and ferromagnetic CoFe, for writing, and spin-to-charge current conversion between CoFe and Pt, for reading. We show that, upon the electrical switching of the BiFeO3, the magnetization of the CoFe can be reversed, giving rise to different voltage outputs. Through additional microscopy techniques, magnetization reversal is linked with the polarization state and antiferromagnetic cycloid propagation direction in the BiFeO3. This study constitutes the building block for magnetoelectric spin-orbit logic, opening a new avenue for low-power beyond-CMOS technologies.

Abstract 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 BaPb0.75Bi0.25O3 electrodes. Notwithstanding the large lattice mismatch between the La-BiFeO3, BaPb0.75Bi0.25O3, 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.

Abstract Chirality or handedness of a material can be used as an order parameter to uncover the emergent electronic properties for quantum information science. Conventionally, chirality is found in naturally occurring biomolecules and magnetic materials. Chirality can be engineered in a topological polar vortex ferroelectric/dielectric system via atomic-scale symmetry-breaking operations. We use four-dimensional scanning transmission electron microscopy (4D-STEM) to map out the topology-driven three-dimensional domain walls, where the handedness of two neighbor topological domains change or remain the same. The nature of the domain walls is governed by the interplay of the local perpendicular (lateral) and parallel (axial) polarization with respect to the tubular vortex structures. Unique symmetry-breaking operations and the finite nature of domain walls result in a triple point formation at the junction of chiral and achiral domain walls. The unconventional nature of the domain walls with triple point pairs may result in unique electrostatic and magnetic properties potentially useful for quantum sensing applications.

Abstract Four-dimensional scanning transmission electron microscopy (4D-STEM) has recently gained widespread attention for its ability to image atomic electric fields with sub-Ångstrom spatial resolution. These electric field maps represent the integrated effect of the nucleus, core electrons and valence electrons, and separating their contributions is non-trivial. In this paper, we utilized simultaneously acquired 4D-STEM center of mass (CoM) images and annular dark field (ADF) images to determine the projected electron charge density in monolayer MoS2. We evaluate the contributions of both the core electrons and the valence electrons to the derived electron charge density; however, due to blurring by the probe shape, the valence electron contribution forms a nearly featureless background while most of the spatial modulation comes from the core electrons. Our findings highlight the importance of probe shape in interpreting charge densities derived from 4D-STEM and the need for smaller electron probes.

Abstract Control and understanding of ensembles of skyrmions is important for realization of future technologies. In particular, the order-disorder transition associated with the 2D lattice of magnetic skyrmions can have significant implications for transport and other dynamic functionalities. To date, skyrmion ensembles have been primarily studied in bulk crystals, or as isolated skyrmions in thin film devices. Here, we investigate the condensation of the skyrmion phase at room temperature and zero field in a polar, van der Waals magnet. We demonstrate that we can engineer an ordered skyrmion crystal through structural confinement on the μm scale, showing control over this order-disorder transition on scales relevant for device applications.

Polar skyrmions are particle-like objects consisted of swirling electric dipoles that hold promise for next generation nanodevices. Here, the authors explore the strain-induced transition from skyrmions to merons using electron imaging methods.

In ferroelectric heterostructures, the interaction between intrinsic polarization and the electric field generates a rich set of localized electrical properties. The local electric field is determined by several connected factors, including the charge distribution of individual unit cells, the interfacial electromechanical boundary conditions, and chemical composition of the interfaces. However, especially in ferroelectric perovskites, a complete description of the local electric field across micro-, nano-, and atomic-length scales is missing. Here, by applying four-dimensional scanning transmission electron microscopy (4D STEM) with multiple probe sizes matching the size of structural features, we directly image the electric field of polarization vortices in (PbTiO3)16/(SrTiO3)16 superlattices and reveal different electric field configurations corresponding to the atomic scale electronic ordering and the nanoscale boundary conditions. The separability of two different fields probed by 4D STEM offers the possibility to reveal how each contributes to the electronic properties of the film.

The polar chiral texture of the vortex or skyrmion structure in ferroelectric oxide PbTiO3/SrTiO3 superlattice attracts attention. Here, the authors report a theoretical framework to probe emergent chirality of electrical polarization textures.

Reducing the switching energy of ferroelectric films remains an important goal. Here, the authors elucidate the fundamental role of lattice dynamics in ferroelectric switching on both freestanding BiFeO3 membranes and films clamped to a substrate.

The response of the electronic structure to the non-trivial polarization texture in PbTiO3/SrTiO3 superlattices has not been explored. Here, the authors reveal how the peaks of the spectra shift and change their local electronic structure depending on the position of the Ti cation.

Abstract Double perovskite oxides, with generalized formula A2BB $$^{\prime}$$ ′ O6, attract wide interest due to their multiferroic and charge transfer properties. They offer a wide range of potential applications such as spintronics and electrically tunable devices. However, great practical limitations are encountered, since a spontaneous order of the B-site cations is notoriously hard to achieve. In this joint experimental-theoretical work, we focused on the characterization of double perovskites La2TiFeO6 and La2VCuO6 films grown by pulsed laser deposition and interpretation of the observed B-site disorder and partial charge transfer between the B-site ions. A random structure sampling method was used to show that several phases compete due to their corresponding configurational entropy. In order to capture a representative picture of the most relevant competing microstates in realistic experimental conditions, this search included the potential formation of non-stoichiometric phases as well, which could also be directly related to the observed partial charge transfer. We optimized the information encapsulated in the potential energy landscape, captured via structure sampling, by evaluating both enthalpic and entropic terms. These terms were employed as a metric for the competition of different phases. This approach, applied herein specifically to La2TiFeO6, highlights the presence of highly entropic phases above the ground state which can explain the disorder observed frequently in the broader class of double perovskite oxides.

Understanding the inner workings of complex magnetoelectric multiferroics remains a challenge, as macroscopic techniques characterize average responses rather than the role of individual iron centers. Here, the authors reveal the origin of high-temperature magnetism in multiferroic superlattices.

BiFeO3 has a wide application but the impact of rare-earth substitution for the evolution of the coupling mechanism is unknown. Here, the authors reveal the correlation between ferroelectricity, antiferromagnetism, a weak ferromagnetic moment, and their switching pathways in La-substituted BiFeO3.

Using epitaxial stabilization, we synthesized single-phase (001)-oriented thin films of DyFe2O4+x on (111) MgAl2O4 substrates by molecular-beam epitaxy. The metastable DyFe2O4 polymorph formed is isostructural to known trigonal ferrimagnetic RFe2O4 phases with space group R3̄m, where R = Ho to Lu. The epitaxial DyFe2O4 thin films have two in-plane orientation relationships: [100] DyFe2O4 || 211̄ MgAl2O4 plus a twin variant related by a 60° in-plane rotation. DyFe2O4 is not bulk stable and has never been synthesized before. Indeed, it has been predicted to be on the edge energetically of what may be possible to stabilize. The fact that the RFe2O4 phase is stable for all elements leading up to dysprosium (Ho–Lu) leads us to believe that DyFe2O4 could be a “remnant metastable phase,” one which, given the right thermodynamic conditions, could become the lowest free energy phase. We find that although we are able to get structurally very close to R3̄m DyFe2O4, the films are not stoichiometric as they have an increased c lattice parameter, indicative of extra oxygen as is sometimes seen in other RFe2O4 phases. The unintended surplus oxygen opens questions regarding what may be achievable using such tricks as epitaxial stabilization to access metastable phases and whether this indeed constitutes “remnant metastability.”

To fully exploit the potential of multiferroic materials the control of their intrinsic degrees of freedom is a prerequisite. Here, the control of spin orientation in strained BiFeO3 films is demonstrated elucidating the microscopic mechanism of the complex interplay of polar and magnetic order.

There is growing interest in the study of thin-film pyroelectric materials because of their potential for high performance thermal-energy conversion, thermal sensing, and beyond. Electrothermal susceptibilities, such as pyroelectricity, are known to be enhanced in proximity to polar instabilities, and this is conventionally accomplished by positioning the material close to a temperature-driven ferroelectric-to-paraelectric phase transition. The high Curie temperature (TC) for many ferroelectrics, however, limits the utility of these materials at room-temperature. Here, the nature of pyroelectric response in thin films of the widely studied multiferroic Bi1−xLaxFeO3 (x = 0–0.45) is probed. While BiFeO3 itself has a high TC, lanthanum substitution results in a chemically induced lowering of the ferroelectric-to-paraelectric and structural-phase transition. The effect of isovalent lanthanum substitution on the structural, dielectric, ferroelectric, and pyroelectric response is investigated using reciprocal-space-mapping studies; field-, frequency-, and temperature-dependent electrical measurements; and phase-sensitive pyroelectric measurements, respectively. While BiFeO3 itself has a rather small pyroelectric coefficient at room temperature (∼−40 µC/m2 K), 15% lanthanum substitution results in an enhancement of the pyroelectric coefficient by 100% which is found to arise from a systematic lowering of TC.

Exploring topological textures in ferroelectrics facilitates the understanding and application of topological features in matter. Here the authors demonstrate the strain field induced evolution of topological vortices in nanoplatelets of rhombohedral phase BiFeO3 using the angle-resolved piezoresponse force microscopy.

Background: Vascular injury is the initial event in the pathogenesis of systemic sclerosis (SSc) and potent proangiogenic mediators such as vascular endothelial growth factor (VEGF) are overexpressed in the skin and circulation of patients with SSc. The objective of this study was to determine the serum levels of VEGF in patients with SSc and to correlate it with the severity of skin thickening, digital ischemia, and interstitial lung disease (ILD). Methods: Serum VEGF levels were measured in 55 patients with SSC who fulfilled 2013 ACR/EULAR classification criteria for scleroderma and 30 healthy age- and gender-matched controls by ELISA. All patients underwent detailed clinical examination, baseline blood investigations, chest X-ray, electrocardiogram, and pulmonary function tests. Echocardiography and high-resolution computed tomography scan of lungs were done wherever necessary. Results: Median serum VEGF in SSc patients was higher than in the controls (675 pg/ml [interquartile range (IQR): 395–920] vs. 180.5 pg/ml [IQR: 155–215], respectively; P = 0.00001). No statistically significant difference was observed between diffuse (662.5 pg/ml [IQR: 441.25–942.5]) and limited SSc (680 pg/ml [IQR: 325–850]) (P = 0.412). Serum VEGF levels correlated significantly with higher modified Rodnan skin scores (r = 0.7168) (P < 0.0001) and lower forced vital capacity (r = −0.6771) (P < 0.0001). Median VEGF levels were higher in patients with digital ischemia (digital pitted scars, digital ulcers, and gangrene) compared to those without ischemic changes (P = 0.001). Patients with ILD (n = 21) had significantly higher median VEGF levels when compared to those without ILD (n = 34) (870 pg/ml [IQR: 592.5–1000] vs. 467.5 pg/ml [IQR: 297.5–760]; P = 0.001). There was no significant difference in serum VEGF levels between early (650 pg/ml [IQR: 375–885]) and late stages (890 pg/ml [IQR: 530–1000]) of disease (P = 0.197). Conclusion: Serum VEGF levels were elevated in SSc and they correlated with the severity of skin thickening, digital ischemia, and presence of ILD.

Background: Assessment of disease activity in axial spondyloarthritis (axSpA) has remained a challenge. This study aims to investigate the role of vascular endothelial growth factor (VEGF) and tumor necrosis factor-alpha (TNF-α) as markers of disease activity in patients with axSpA. Methods: A total of 40 patients with axSpA were included in this study. Erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), Bath Ankylosing Spondylitis Disease Activity Index (BASDAI)/Bath Ankylosing Spondylitis Functional Index (BASFI), serum TNF-α, and VEGF levels were assessed at baseline and the same parameters were assessed after 24 weeks of therapy with either etanercept or NSAIDs (20 patients in each group). Twenty healthy age- and sex-matched controls were also recruited for the study. Results: Patients with axSpA had higher levels of serum TNF-α (mean 341 pg/ml) and VEGF (mean 791 pg/ml) as compared with healthy controls (mean 72.5 pg/ml, P < 0.001 and mean 269 pg/ml, P < 0.001). There was significant reduction in serum TNF-α and VEGF levels after 24 weeks of treatment with etanercept (mean 161 pg/ml, P < 0.001 and mean 442 pg/ml, P < 0.001, respectively) but not with NSAID (P = 0.29, P = 0.25). Both TNF-α and VEGF had a positive correlation with BASDAI (r = 0.57, P < 0.01 and r = 0.44, P < 0.01) and BASFI (r = 0.61, P < 0.01 and r = 0.33, P = 0.03) at baseline. The levels of TNF-α and VEGF showed no correlation with ESR and CRP (P = 0.48, P = 0.07 and P = 0.21, P = 0.06, respectively) at baseline. There was no correlation between BASDAI and levels of ESR, CRP (P = 0.27 and P = 0.49, respectively). Conclusion: Serum levels of TNF-α and VEGF serve as better markers of disease activity as compared with ESR and CRP in axSpA.

Background: Immune dysregulation triggered by environmental events (including microbes) have been implicated in the etiopathogenesis of systemic sclerosis (SSc). Helicobacter pylori (H. pylori) a pathogen well known to cause gastric ulcers and has been associated with several autoimmune diseases. However, the role of H. pylori in SSc has not been widely reported. The objective of the study was to estimate the prevalence of H. pylori infection in SSc patients and analyze its clinical associations. Methods: This study comprised 55 patients who satisfied ACR/EULAR 2013 classification criteria for SSc and 25 age and sex-matched healthy controls. Demographic, clinical, laboratory, and immunological parameters were recorded. Upper gastrointestinal (GI) endoscopy was done. Anti-H. pylori IgG levels (RU/ml) were estimated by ELISA and results analyzed by SPSS. Results: Baseline characteristics were comparable in both groups. Prevalence of H. pylori infection was high in SSc patients in comparison to controls (61.8% vs. 24%). Anti-H. pylori IgG levels were high in SSc patients in comparison to controls (mean 65 RU/ml vs. 25.3RU/ml; P = 0.003). SSc patients with symptomatic GI involvement had higher anti-H. pylori IgG levels than asymptomatic patients (mean 118.3 RU/ml vs. 20.7 RU/ml; P < 0.001). Anti-H. pylori IgG levels were not significantly different between diffuse cutaneous SSc and limited cutaneous SSc (mean 72.9 RU/ml vs. 54.1RU/ml; P = 0.289). Anti-H. pylori IgG antibody levels showed no correlation with disease duration, erythrocyte sedimentation rate, C-reactive protein, interstitial lung disease, and modified Rodnan Skin Score. Conclusion: SSc patients have high seropositivity for anti-H. pylori IgG antibodies. High anti-H. pylori IgG antibody titers are associated with symptomatic upper GI dysfunction.

Ferroelastic switching in thin films is typically restricted by constraints from the substrate or occurs around twin-like domains. Here, the authors show reversible and non-volatile ferroelastic switching avoiding substrate constraints in layered-perovskite Bi_2WO_6 epitaxial films.

Synthesis of single-crystal complex-oxide films directly on silicon is difficult due to differing interfacial chemistry. Here, the authors demonstrate room-temperature integration of single-crystal lead zirconate titanate on to silicon to act as a gate insulator in a field-effect transistor.

Scaling-up solutions require learning and adapting lessons between locations and at different scales. To accomplish this, common metrics are vital to building a shared language. For California, this has meant careful financial, cradle-to-grave life-cycle assessment methods leading to carbon accounting in many avenues of government (via the Low Carbon Fuel Standard or the Cap and Trade program). These methods themselves interact, such as the use of carbon accounting for the resources needed to manage water and other key resources; the use of criteria air pollution monitoring to identify environmental injustices; and the use of carbon market revenues to address these inequalities, through investment in best available abatement technologies (BACT) and in job creation in disadvantaged communities anticipated in the emerging clean energy sector. Creating interdisciplinary partnerships across the UC Campuses and the National Laboratories to innovate science and technology is critical to scalable carbon neutrality solutions. As an example, we can build coordinated research and development programs across UC and California, with strong partnerships with the Federal government to coordinate and “multiply” resources that accelerate development and deployment. These partnerships should be strongly goal-focused, i.e., they are created to solve specific, large problems, to enable quantitatively measurable outcomes within energy generation, efficiency and CO2 abatement categories. Intersectoral partnerships should be fostered across campuses, laboratories, with state, federal and multi-lateral organizations funding to develop technologies and deploy solutions at scale. Integrated partnerships with industry are required to influence markets, deploy solutions, and create new industries and jobs. Beyond California, we need to establish consortia with industry and foundations to deploy solutions at the regional, state, national, and international scale to create new industries, new jobs, and further UC and California’s leadership position. Significant economic opportunities exist, such as promoting aggressive electric vehicle programs elsewhere in the world, where California-based companies could play a key role on many fronts, via electric vehicles themselves, but also through building-integrated smart meters, inverters, solar and other clean energy generation technologies. All work must include a focus on environmental justice both at home in California and through global partnerships.