arXiv subjects

Elzbieta Gradauskaite

Publications and source records attributed to Elzbieta Gradauskaite.

12 recordsLinked to original sources

arXiv2026

Chemical heterogeneity at conducting ferroelectric domain walls

Natural interfaces in ferroic oxides have developed into versatile playgrounds for studying electronic correlation effects in 2D systems. The microscopic origin of the emergent local electronic properties is often debated, however, as quantitative atomic-scale characterization remains challenging. A prime example is enhanced conductivity at ferroelectric domain walls, attributed to mechanisms ranging from local band gap reduction to point defect accumulations. Here, we resolve the microscopic mechanisms for domain wall conduction in the ferroelectric model system BiFeO3, by combining transport measurements with atom probe tomography to quantify the local chemical composition and correlate it with the electrical properties. Significant chemical variations along the walls are observed, demonstrating an outstanding chemical flexibility at domain walls, which manifest in spatially varying physical properties. The results give a unifying explanation for the diverse electronic behavior observed and establish the fundamental notion that multiple conduction mechanisms can coexist within individual domain walls.

cond-mat.mtrl-sci↗

arXiv2025

Control of polarization and polar chiral textures in BiFeO$_3$ by epitaxial strain and interfacial chemistry

The balance between interfacial chemistry, electrostatics, and epitaxial strain plays a crucial role in stabilizing polarization in ferroelectric thin films. Here, we bring these contributions into competition in BiFeO$_3$ (BFO) thin films grown on the charged-surface-terminated La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO)-buffered NdGaO$_3$ (001) substrates. The large anisotropic compressive strain from the substrate promotes the formation of ferroelectric domains despite the expected stabilization of a uniform out-of-plane polarization by the (La,Sr)O$^{0.7+}$ termination of the metallic buffer. Piezoresponse force microscopy and scanning transmission electron microscopy reveal that the resulting nanoscale domain architecture is stabilized by the deterministic formation of a fluorite-like Bi$_2$O$_2$ surface layer on regions polarized oppositely to the LSMO-imposed polarization orientation. Leveraging this polarization compensation mechanism, we stabilize a uniform out-of-plane polarization in our highly strained BFO films by inserting a Bi$_2$O$_2$-terminated Aurivillius film as a buffer layer. Additionally, we reveal signatures of homochiral polarization textures in our BFO films on the level of domain configurations using local polarization switching experiments. Our work thus brings new strategies for controlling polarization direction and chiral textures in oxide ferroelectrics, opening pathways for functional domain-wall and domain-based electronics.

cond-mat.mtrl-sci↗

arXiv2025

Revival of Layered Ferroelectrics in Thin Films

Layered perovskites are a versatile class of ferroelectrics with their structural anisotropy reflected in unusual electrostatics that give rise to exceptional ferroelectric properties. These materials fall into four main families: Aurivillius, Carpy-Galy, Ruddlesden-Popper, and Dion-Jacobson phases; each forming natural superlattices by interleaving perovskite slabs with spacer layers. For a long time, these materials were considered too structurally complex to prepare as high-quality thin films. However, recent breakthroughs in deposition and advanced characterization have made it possible to stabilize high-quality films with atomic precision, uncovering a wide range of unconventional ferroelectric functionalities. These include robust in-plane polarization without a critical thickness, the emergence of charged domain walls and non-trivial polar textures, resilience to doping with magnetic ions and charge carriers, and possibility to epitaxially integrate them into standard perovskite heterostructures. This review aims to unify current knowledge on the fabrication and characterization of layered ferroelectric thin films, and to present research findings across all four structural families, with the goal of highlighting their common features despite differences in crystal structure and polarization mechanisms. We also discuss promising research directions, including polar metallicity, (alter-)magnetoelectricity, exfoliation, and soft-chemistry-driven phase transformations, with the goal of consolidating the field and encouraging further exploration of these materials for both fundamental studies and applications.

cond-mat.mtrl-sci↗

arXiv2025

Nanoscale electrostatic control in ferroelectric thin films through lattice chemistry

Nanoscale electrostatic control of oxide interfaces enables physical phenomena and exotic functionalities beyond the realm of the bulk material. In technologically-relevant ferroelectric thin films, the interface-mediated polarization control is usually exerted by engineering the depolarizing field. Here, in contrast, we introduce polarizing surfaces and lattice chemistry engineering as an alternative strategy. Specifically, we engineer the electric-dipole ordering in ferroelectric oxide heterostructures by exploiting the charged sheets of the layered Aurivillius model system. By tracking in-situ the formation of the Aurivillius charged Bi$_{2}$O$_{2}$ sheets, we reveal their polarizing effect leading to the characteristic Aurivillius out-of-plane antipolar ordering. Next, we use the polarizing Bi$_{2}$O$_{2}$ stacking as a versatile electrostatic environment to create new electric dipole configurations. We insert multiferroic BiFeO$_3$ into the Aurivillius framework to stabilize a ferrielectric-like non-collinear electric-dipole order in the final heterostructure while maintaining the antiferromagnetic order of BiFeO$_3$. We thus demonstrate that engineering the lattice chemistry stabilizes unconventional ferroic orderings at the nanoscale, a strategy that may be expanded beyond the realm of electrically ordered materials.

cond-mat.mtrl-sci↗

arXiv2024

Polarization boost and ferroelectricity down to one unit cell in layered Carpy-Galy La$_{2}$Ti$_{2}$O$_{7}$ thin films

Layered perovskite-based compounds offer a range of unconventional properties enabled by their naturally anisotropic structure. While most renowned for the superconductivity observed in the Ruddlesden-Popper phases, many of these layered compounds are also ferroelectric and exhibit a sizeable in-plane polarization. Among these, the Carpy-Galy phases (A${_n}$B${_n}$O$_{3n+2}$), characterized by 110-oriented perovskite planes interleaved with additional oxygen layers, have been debated as platforms for hosting not only a robust polarization but also multiferroicity and polar metallicity. However, the challenges associated with the synthesis of ultrathin Carpy-Galy films and understanding the impact of strain on their properties limit their integration into devices. Addressing this issue, our study focuses on La$_2$Ti$_2$O$_7$, an $n$=4 (A$_2$B$_2$O$_7$) representative of the Carpy-Galy family, exploring its growth and concurrent phase stability on various substrates under different strain conditions. Remarkably, we demonstrate that a 3% tensile strain from DyScO$_3$ (100) substrates promotes a controlled layer-by-layer growth mode, while SrTiO$_3$ (110) and LaAlO$_3$-Sr$_2$TaAlO$_6$ (110), that exert negligible and compressive strains respectively, require post-deposition annealing to achieve similar results. Using scanning probe microscopy, X-ray diffraction, scanning transmission electron microscopy, and polarization switching experiments, we confirm that these films possess exceptional ferroelectric properties, including a polarization of 18 $μ$C/cm$^2$ - more than three times higher than previously reported - as well as persistence of ferroelectricity down to a single-unit-cell thickness. This study not only advances our understanding of Carpy-Galy phases in thin films but also lays a foundation for their application in advanced ferroelectric device architectures.

cond-mat.mtrl-sci↗

arXiv2024

Magnetoelectric phase control at domain-wall-like epitaxial oxide multilayers

Ferroelectric domain walls are nanoscale objects that can be created, positioned, and erased on demand. They often embody functional properties that are distinct from the surrounding bulk material. Enhanced conductivity, for instance, is observed at charged ferroelectric domain walls. Regrettably, domain walls of this type are scarce because of the energetically unfavorable electrostatics. This hinders the current technological development of domain-wall nanoelectronics. Here we overcome this constraint by creating robust domain-wall-like objects in epitaxial oxide heterostructures. We design charged head-to-head (HH) and tail-to-tail (TT) junctions with two ferroelectric layers (BaTiO$_{3}$ and BiFeO$_{3}$) that have opposing out-of-plane polarization. To test domain-wall-like functionalities, we insert an ultrathin ferromagnetic La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ layer into the junctions. The interfacial electron or hole accumulation at the interfaces, set by the HH and TT polarization configurations, respectively, controls the LSMO conductivity and magnetization. We thus propose that trilayers reminiscent of artificial domain walls provide magnetoelectric functionality and may constitute an important building block in the design of oxide-based electronic devices.

cond-mat.mtrl-sci↗

arXiv2024

Magnetoelectric domain engineering from micrometer to Ångstrøm scales

The functionality of magnetoelectric multiferroics depends on the formation, size, and coupling of their magnetic and electric domains. Knowing the parameters guiding these criteria is a key effort in the emerging field of magnetoelectric domain engineering. Here we show, using a combination of piezoresponse-force microscopy, non-linear optics, and x-ray scattering, that the correlation length setting the size of the ferroelectric domains in the multiferroic hexagonal manganites can be engineered from the micron range down to a few unit cells under the substitution of Mn$^{3+}$ ions with Al$^{3+}$ ions. The magnetoelectric coupling mechanism between the antiferromagnetic Mn$^{3+}$ order and the distortive-ferroelectric order remains intact even at substantial replacement of Mn$^{3+}$ by Al$^{3+}$. Hence, chemical substitution proves to be an effective tool for domain-size engineering in one of the most studied classes of multiferroics.

cond-mat.mtrl-sci↗

arXiv2023

Current-driven dynamics and ratchet effect of skyrmion bubbles in a ferrimagnetic insulator

Magnetic skyrmions are compact chiral spin textures that exhibit a rich variety of topological phenomena and hold potential for developing high-density memory devices and novel computing schemes driven by spin currents. Here, we demonstrate room temperature interfacial stabilization and current-driven control of skyrmion bubbles in the ferrimagnetic insulator Tm3Fe5O12 (TmIG) coupled to Pt. We track the current-induced motion of individual skyrmion bubbles. The ferrimagnetic order of the crystal together with the interplay of spin-orbit torques and pinning determine the skyrmion dynamics in TmIG and result in a strong skyrmion Hall effect characterized by a negative deflection angle and hopping motion. Further, we show that the velocity and depinning threshold of the skyrmion bubbles can be modified by exchange coupling TmIG to an in-plane magnetized Y3Fe5O12 layer, which distorts the spin texture of the skyrmions and leads to a directional-dependent rectification of their dynamics. This effect, which is equivalent to a magnetic ratchet, is exploited to control the skyrmion flow in a racetrack-like device.

cond-mat.mes-hall↗

arXiv2022

Defeating depolarizing fields with artificial flux closure in ultrathin ferroelectrics

Material surfaces encompass structural and chemical discontinuities that often lead to the loss of the property of interest in the so-called dead layers. It is notably problematic in nanoscale oxide electronics, where the integration of strongly correlated materials into devices is obstructed by the thickness threshold required for the emergence of their functionality. Here, we report the stabilization of ultrathin out-of-plane ferroelectricity in oxide heterostructures through the design of an artificial flux-closure architecture. Inserting an in-plane polarized ferroelectric epitaxial buffer provides continuity of polarization at the interface, and despite its insulating nature we observe the emergence of polarization in our out-of-plane-polarized model ferroelectric BaTiO$_{3}$ from the very first unit cell. In BiFeO$_{3}$, the flux-closure approach stabilizes a conceptually novel 251$^{\circ}$ domain wall. Its unusual chirality is likely associated with the ferroelectric analog to the Dzyaloshinskii-Moriya interaction. We thus see that in an adaptively engineered geometry, the depolarizing-field-screening properties of an insulator can even surpass those of a metal and be a source of new functionalities. This should be a useful insight on the road towards the next generation of ferroelectric-based oxide electronics.

cond-mat.mtrl-sci↗

arXiv2022

Combined electrostatic and strain engineering of BiFeO$_3$ thin films at the morphotropic phase boundary

Multiferroic BiFeO$_3$ (BFO) possesses a rich phase diagram that allows strain tuning of its properties in thin-film form. In particular, at large compressive strain, a supertetragonal (T) phase with giant polarization is stabilized over the more common rhombohedral (R) structure. To utilize the functionality of such metastable BFO phases in device applications, it is essential to understand the ferroelectric phase evolution upon insertion in nanoscale heterostructures. Here, we explore the emergence of ferroelectric phases close to the morphotropic phase boundary in compressively strained BFO during thin-film growth using in-situ optical second harmonic generation. We find that the epitaxial films form at the growth temperature in the ideal T phase without critical thickness for the polarization. Signatures of T-like and R-like monoclinically distorted phases only appear upon sample cooling. We furthermore demonstrate a robustness of single-domain polarization in the high-temperature T phase during the growth of capacitor-like metal|ferroelectric|metal heterostructures. Here, a reduction in tetragonality of the T phase, rather than domain formation, lowers the electrostatic energy. At this lower tetragonality, density-functional calculations and scanning transmission electron microscopy point to the stabilization of a new metastable R-like monoclinic structure upon cooling the heterostructure down to room temperature. Our results thus show that the combination of strain and electrostatic phase stabilization in BFO heterostructures yields a prominent platform for exploring ferroelectric phases and realizing ultrathin ferroelectric devices.

cond-mat.mtrl-sci↗

arXiv2019

High-speed domain wall racetracks in a magnetic insulator

Recent reports of current-induced switching of ferrimagnetic oxides coupled to a heavy metal layer have opened realistic prospects for implementing magnetic insulators into electrically addressable spintronic devices. However, key aspects such as the configuration and dynamics of magnetic domain walls driven by electrical currents in insulating oxides remain unexplored. Here, we investigate the internal structure of the domain walls in Tm3Fe5O12 (TmIG) and TmIG/Pt bilayers and demonstrate their efficient manipulation by spin-orbit torques with velocities of up to 400 m s$^{-1}$ and minimal current threshold for domain wall flow of 5 x 10$^{6}$ A cm$^{-2}$. Domain wall racetracks embedded in TmIG are defined by the deposition of Pt current lines, which allow us to control the domain propagation and magnetization switching in selected regions of an extended magnetic layer. Scanning nitrogen-vacancy magnetometry reveals that the domain walls of thin TmIG films are Néel walls with left-handed chirality, with the domain wall magnetization rotating towards an intermediate Néel-Bloch configuration upon deposition of Pt. These results indicate the presence of a sizable interfacial Dzyaloshinskii-Moriya interaction in TmIG, which leads to novel possibilities to control the formation of chiral spin textures in magnetic insulators. Ultimately, domain wall racetracks provide an efficient scheme to pattern the magnetic landscape of TmIG in a fast and reversible way

physics.app-ph↗

arXiv2017

PbTi1-xPdxO3: A New Room-temperature Magnetoelectric Multiferroic Device Material

There have been a large number of papers on bismuth ferrite (BiFeO3) over the past few years, trying to exploit its room-temperature magnetoelectric multiferroic properties. Although these are attractive, BiFeO3 is not the ideal multiferroic, due to weak magnetization and the difficulty in limiting leakage currents. Thus there is an ongoing search for alternatives, including such materials as gallium ferrite (GaFeO3). In the present work we report a comprehensive study of the perovskite PbTi1-xPdxO3 with 0 < x < 0.3. Our study includes dielectric, impedance and magnetization measurements, conductivity analysis and study of crystallographic phases present in the samples with special attention paid to minor phases, identified as PdO, PbPdO2, and Pd3Pb. The work is remarkable in two ways: Pd is difficult to substitute into ABO3 perovskite oxides (where it might be useful for catalysis), and Pd is magnetic under only unusual conditions (under strain or internal electric fields). The new material, as a PZT derivative, is expected to have much stronger piezoelectric properties than BiFeO3.

cond-mat.mtrl-sci↗