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 BiFeO3are 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 BiFeO3in 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.
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Abstract Free, publicly-accessible full text available December 1, 2025 -
Hierarchical assemblies of ferroelectric nanodomains, so-called super-domains, can exhibit exotic morphologies that lead to distinct behaviours. Controlling these super-domains reliably is critical for realizing states with desired functional properties. Here we reveal the super-switching mechanism by using a biased atomic force microscopy tip, that is, the switching of the in-plane super-domains, of a model ferroelectric Pb0.6Sr0.4TiO3. We demonstrate that the writing process is dominated by a super-domain nucleation and stabilization process. A complex scanning-probe trajectory enables on-demand formation of intricate centre-divergent, centre-convergent and flux-closure polar structures. Correlative piezoresponse force microscopy and optical spectroscopy confirm the topological nature and tunability of the emergent structures. The precise and versatile nanolithography in a ferroic material and the stability of the generated structures, also validated by phase-field modelling, suggests potential for reliable multi-state nanodevice architectures and, thereby, an alternative route for the creation of tunable topological structures for applications in neuromorphic circuits.more » « lessFree, publicly-accessible full text available September 26, 2025
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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.
Free, publicly-accessible full text available December 1, 2025 -
There is an increasing desire to utilize complex functional electronic materials such as ferroelectrics in next-generation microelectronics. As new materials are considered or introduced in this capacity, an understanding of how we can process these materials into those devices must be developed. Here, the effect of different fabrication processes on the ferroelectric and related properties of prototypical metal oxide (SrRuO3)/ferroelectric (BaTiO3)/metal oxide (SrRuO3) heterostructures is explored. Two different types of etching processes are studied, namely, wet etching of the top SrRuO3 using a NaIO4 solution and dry etching using an Ar+-ion beam (i.e., ion milling). Polarization-electric-field hysteresis loops for capacitors produced using both methods are compared. For the ion-milling process, it is found that the Ar+ beam can introduce defects into the SrRuO3/BaTiO3/SrRuO3 devices and that the milling depth strongly influences the defect level and can induce a voltage imprint on the function. Realizing that such processing approaches may be necessary, work is performed to ameliorate the imprint of the hysteresis loops via ex situ “healing” of the process-induced defects by annealing the ferroelectric material in a barium-and-oxygen-rich environment via a chemical-vapor-deposition-style process. This work provides a pathway for the nanoscale fabrication of these candidate materials for next-generation memory and logic applications.
Free, publicly-accessible full text available April 1, 2025 -
Understanding the microscopic origin of the superior electromechanical response in relaxor ferroelectrics requires knowledge not only of the atomic-scale formation of polar nanodomains (PNDs) but also the rules governing the arrangements and stimulated response of PNDs over longer distances. Using x-ray coherent nanodiffraction, we show the staggered self-assembly of PNDs into unidirectional mesostructures that we refer to as polar laminates in the relaxor ferroelectric 0.68PbMg1/3Nb2/3O3-0.32PbTiO3(PMN-0.32PT). We reveal the highly heterogeneous electric-field–driven responses of intra- and interlaminate PNDs and establish their correlation with the local strain and the nature of the PND walls. Our observations highlight the critical role of hierarchical lattice organizations on macroscopic material properties and provide guiding principles for the understanding and design of relaxors and a wide range of quantum and functional materials.
Free, publicly-accessible full text available June 28, 2025 -
Free, publicly-accessible full text available July 16, 2025
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The bulk photovoltaic effect (BPE) has drawn considerable attention due to its ability to generate photovoltages above the bandgap and reports of highly enhanced photovoltaic current when using nanoscale absorbers or nanoscale electrodes, which, however, do not lend themselves to practical, scalable implementation. Herein, it is shown that a strikingly high BPE photoresponse can be achieved in an ordinary thin‐film configuration merely by tuning fundamental ferroelectric properties. Nonmonotonic dependence of the responsivity (
R SC) on the ferroelectric polarization is observed and at the optimal value of the film polarization, a more than three orders of magnitude increase in theR SCfrom the bulk BaTiO3value is obtained, reachingR SCclose to 10−2 A W−1, the highest value reported to date for the archetypical ferroelectric BaTiO3films. Results challenge the applicability of standard first‐principles‐based descriptions of BPE to thin films and the inherent weakness of BPE in ferroelectric thin films. -
Further miniaturization of electronic devices necessitates the introduction of new materials, including piezoelectric thin films, that exhibit electromechanical functionalities without significant degradation in response due to substrate-induced clamping. To identify material systems with superior piezoelectric properties as thin films, simplified and quantitative electromechanical characterization techniques are required. Here, single-beam, laser Doppler vibrometry is used to detect ac electric-field-induced surface displacement in the frequency range 1–100 kHz with low error (around 6% at 10 kHz) and resolution of 0.0003 nm. The technique is used to quantify both electrostriction and piezoelectric responses (surface displacement values <0.05 nm) of various thin films. Requirements for sample geometry and device structures are established and measurement accuracy and resolution are validated against measurements from the literature via synchrotron-based diffraction measurements. A general methodology to measure and extract the piezoelectric coefficients for thin-film samples using finite-element modeling is presented and applied to determine the d33 coefficient and visualize the response in substrate-clamped 50–400-nm-thick PbZr0.52Ti0.48O3 films, especially as compared to bulk versions with the same sample geometry.more » « less
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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.
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Abstract Bismuth ferrite has garnered considerable attention as a promising candidate for magnetoelectric spin-orbit coupled logic-in-memory. As model systems, epitaxial BiFeO3thin 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 BiFeO3at 450 °C (which is reasonably compatible with silicon-CMOS integration) on epitaxial BaPb0.75Bi0.25O3electrodes. 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 SrRuO3typically 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.