Stripe Domains Research Articles

Kinetics of the Domain Structure in Uniform Electric Field in LiNbO3 with Surface Layer Modified by Soft Proton Exchange

The creation of periodic domain structures in lithium niobate crystals makes it possible to realize highly efficient nonlinear optical interactions in optical waveguides. The influence of near‐surface H+ ion concentration gradient on the domain kinetics in uniform electric field in lithium niobate crystals modified by soft proton exchange is studied. The spatial distribution of the H+ ions concentration in the surface layer is obtained by confocal Raman microscopy. The observed anomalous evolution of the domain structure at the surface represents the formation of stripe domains and their anisotropic growth along three directions. The domain imaging in the bulk allows revealing a comb‐like domain shape. The obtained strong influence of the proton exchange duration on the threshold field is attributed to the action of the concentration gradient in the near‐surface layer, which is considered as an analog of the internal bias electric field. It is shown that the internal bias field is proportional to the increase in the concentration gradient in the surface layer. The mechanism of the comb‐like domain formation is proposed. The obtained results can be used for development of domain engineering methods in optical waveguides.

Skyrmion Based Synaptic Device Having Perpendicular Magnetic-Tunnel-Junction Spin-Valve Sensor

Perpendicular spin-transfer-torque magnetic random access memory (p-STT MRAM) has been reported as an application of binary neural networks (BNN) [1]. In addition, magnetic skyrmions have been reported as information carriers for neuromorphic devices due to their small nanoscale diameter, topological stability, and complete linearity [2-3]. A previous study has demonstrated the synaptic characteristics of skyrmion based synapses using a Hall bar measurement [4]. However, skyrmion based synapses using the Hall bar measurement were not able to detect electrically a synaptic behavior. Thus, for the first time, the skyrmion based synaptic device detected resistance change via sensing the perpendicular magnetic-tunnel-junction (p-MTJ) spin-valve, as shown in Fig.1(a). The detailed synaptic behavior and mechanism will be presented.In this study, we introduced the skyrmion based synaptic device having p-MTJ spin-valve sensor designed by CoFeB free layer, MgO tunneling barrier, CoFeB pinned layer, SyAF layer, and interface reducing W layer between the CoFeB free layer and MgO tunneling barrier, as shown in Fig.1(a). The spin direction of the CoFeB free layer was changed by the generated skyrmions, and the resistance of the synaptic device changed depending on the parallel or anti-parallel state between CoFeB free and pinned layer. In particular, the skyrmion generation was determined critically by the combination of DMI and PMA (i.e., saturation magnetization (Ms), squareness), and the interface reducing W layer was designed to reduce PMA. The M-H loop of the synaptic device with the interface reducing W layer thickness of 0.110 nm showed reduced saturation magnetization (Ms ~ 60 μemu) and squareness (Hc ~ 8 Oe) via a vibrating-sample magnetometer (VSM), as shown in [Figs.1(b), 1(c), and 1(d)]. In addition, uniform state, generation of skyrmions, and stripe domains in the synaptic device were achieved at the external magnetic field of 0, 3.5, and 7 Oe, respectively, as shown in [Figs.1(e), 1(f), and 1(g)]. Moreover, we observed that the number of skyrmions in the synaptic device with a cell diameter of 5μm changed depending on the external magnetic field via the magneto-optical Kerr effect (MOKE) image, as shown in [Figs.1(h), 1(i), and 1(j)]. Finally, we demonstrated a multi-level operation in which the electrical resistance of the synaptic device changed as the number of skyrmions. In our presentation, we will review in detail the synaptic behavior and mechanism for the synaptic device. Acknowledgements This research was supported by National R&D Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (2021M3F3A2A01037733) References [1] Thi-Nhan Pham et al., IEEE JOURNAL ON EMERGING AND SELECTED TOPICS IN CIRCUITS AND SYSTEMS, 12, 569-579 (2022)[2] Nagaosa, N. & Tokura, Y. Nat. Nanotechnol. 8, 899–911 (2013).[3] C Back, V Cros et al., J. phys. D. Appl. phys. 53, 363001 (2020).[4] Kyung Mee Song et al., Nature Electronics. 3, 148–155 (2020) Figure 1

Magnitno-silovaya i nelineyno-opticheskaya mikroskopiya pripoverkhnostnoy domennoy struktury epitaksial'noy plenki ferrita-granata

The magnetic properties of the surface layer of an epitaxial bismuth-doped iron garnet film with a weak uniaxial anisotropy are studied by magnetic force, optical, and nonlinear optical microscopy. A significant modulation of optical second harmonic generation intensity along stripe domains is detected near the free film surface. This modulation is caused by periodic distortions of the stripe domain structure near the film surface and the presence of surface closure domains detected by magnetic force microscopy (MFM). A series of MFM images of the film taken in an in-plane magnetic field varying from –400 to 400 Oe demonstrates quasi-static nucleation of closure domains periodically located along stripe domains.

Tuning vortex critical velocity in Mo2N thin films via striped magnetic domain configuration

We report on the impact of the magnetic domain stripe configuration on the critical velocity of vortices in superconducting/ferromagnetic bilayers. Using a 23 nm thick Mo2N film, covered by a 48 nm FePt layer with tunable nanosized striped domains, we demonstrate that flux instability at low magnetic fields depends on the orientation of the stripes. When the stripes are perpendicular to the applied current and act as vortex guides, the velocity values reach 5 km/s, duplicating those found when configured parallel to the current, creating intricate vortex trajectories. Our results indicate that vortex critical velocities can be tuned by configuring different domain structures, providing a platform to understand vortex dynamics in superconducting microstrips.

Artificial magnetic disclination through local stress engineering

Magnetic disclination, characterized by the orientation of domain-wall arrangement rotating by π along a closed loop, is a type of topological spin texture. This study demonstrates the creation of artificial magnetic disclination through local stress engineering. By patterning nanotrenches in permalloy/poly(methyl methacrylate) bilayers, the tensile stress is relieved in a directional manner through the formation of boundaries. This orients the domain distributions at the microscale through magnetoelastic coupling. Two-dimensional (2D) closed boundaries induce curved stripe domains, which are ultimately converted into disclinations. The geometric configuration and arrangement of the disclination can be spatially adjusted via 2D boundary designation. The combination of in-situ magnetic force microscopy and hysteresis loop measurements links the microscopic domain configuration to the macroscopic magnetic properties of the system. Simulations reveal that the magnetic disclination is critically dominated by the local stress distribution within the topographic confinement.

Smectic layers reorientation with stripes and heliconical structure in surface stabilised ferroelectric liquid crystal

ABSTRACT High-tilt angle ferroelectric liquid crystal material in surface stabilised geometry (SSFLC) is investigated for the smectic layer reorientation and its molecular dynamics by electro-optical and dielectric spectroscopy techniques. Smectic layer reorientation (5 o to 45 o ) is obtained by controlled cooling rate and applying electric field in the vicinity of transition temperature from chiral nematic ( N ∗ ) to chiral smectic C ( Sm C ∗ ) phase. After slow cooling down to room temperature, the stripe domain textures along the rubbing are observed with quasi-bistable states. Dielectric spectroscopy has revealed the unusual increment in the dielectric permittivity. A dielectric relaxation process at lower frequency than Goldstone mode with the increase in DC bias up to 2 V is observed in the sample cooled without any bias. This increment is found to be originated by the heliconical structure within the stripes which is seen in the optical textures recorded at the time of dielectric scan. However, this increment is not observed in the sample cooled under DC bias. Thus, there exist different phenomena in the high tilt angle SSFLC sample cooled in different conditions of DC bias; stripe domains, smectic layers reorientation, heliconical stricture and twisted structure within stripes which are significant to explore deeply in high-tilt angle ferroelectric liquid crystals.

Manipulating the Magnetic Bubbles and Topological Hall Effect in 2D Magnet Fe5GeTe2

AbstractRecent observations of nontrivial spin textures and topological Hall effect (THE) in 2D van der Waals (vdW) ferromagnets have stimulated high interest in both fundamental physics and prospective spintronic applications. However, effectively manipulating spin textures and their exhibiting THE, which is the prerequisite for topology‐based 2D vdW devices, remains challenging. Here, the effective manipulation of the magnetic bubbles and THE is achieved in Fe5GeTe2 (FGT) crystals by utilizing Lorentz imaging and electrical transport measurements. The density and size of magnetic bubbles can be modulated effectively as the temperature and lamella thickness change, indicating the role of magnetocrystalline anisotropy and long‐range magnetic dipolar interaction is demonstrated, respectively. More importantly, the spin configurations of bubbles along with THE signal vary with sample thickness, demonstrating a topological transition between skyrmion bubbles and trivial bubbles. The key point lies in the presence or absence of Bloch lines in the stripe domain at different thicknesses. This study presents the reliable manipulations of spin textures and THE in FGT, which may provide valuable insights into the design of 2D vdW devices in spintronics.

Studying the Crucial Physical Characteristics Related to Surface Roughness and Magnetic Domain Structure in CoFeSm Thin Films

This study investigated the effects of varying film thicknesses and annealing temperatures on the surface roughness and magnetic domain structure of CoFeSm thin films. The results revealed that as the film thickness increased, both the crystalline size and surface roughness decreased, leading to a reduction in coercivity (Hc) and improved magnetic contrast performance. Energy-dispersive X-ray spectroscopy (EDS) analysis confirmed the presence of cobalt (Co), iron (Fe), and samarium (Sm) within the thin films. Notably, the 40 nm Co40Fe40Sm20 thin film annealed at 200 °C exhibited lower sheet resistance (Rs) and resistivity (ρ), indicating higher conductivity and a relatively higher maximum magnetic susceptibility (χac) at 50 Hz. These findings suggest that these films are well suited for low-frequency magnetic components due to their increased spin sensitivity. The 40 nm Co40Fe40Sm20 thin film, subjected to annealing at 200 °C, displayed a distinct stripe domain structure characterized by prominently contrasting dark and bright patterns. It exhibited the lowest Hc and the highest saturation magnetization (Ms), leading to a significant improvement in their soft magnetic properties. It is proposed that the surface roughness of the CoFeSm thin films plays a crucial role in shaping the magnetic properties of these thin magnetic films.

Engineering Relaxor Behavior in (BaTiO3 )n /(SrTiO3 )n Superlattices.

Complex-oxide superlattices provide a pathway to numerous emergent phenomena because of the juxtaposition of disparate properties and the strong interfacial interactions in these unit-cell-precise structures. This is particularly true in superlattices of ferroelectric and dielectric materials, wherein new forms of ferroelectricity, exotic dipolar textures, and distinctive domain structures can be produced. Here, relaxor-like behavior, typically associated with the chemical inhomogeneity and complexity of solid solutions, is observed in (BaTiO3 )n /(SrTiO3 )n (n = 4-20 unit cells) superlattices. Dielectric studies and subsequent Vogel-Fulcher analysis show significant frequency dispersion of the dielectric maximum across a range of periodicities, with enhanced dielectric constant and more robust relaxor behavior for smaller period n. Bond-valence molecular-dynamics simulations predict the relaxor-like behavior observed experimentally, and interpretations of the polar patterns via 2D discrete-wavelet transforms in shorter-period superlattices suggest that the relaxor behavior arises from shape variations of the dipolar configurations, in contrast to frozen antipolar stripe domains in longer-period superlattices (n = 16). Moreover, the size and shape of the dipolar configurations are tuned by superlattice periodicity, thus providing a definitive design strategy to use superlattice layering to create relaxor-like behavior which may expand the ability to control desired properties in these complex systems.

The iron garnet stripe domain structure “refraction” effect at the electrode location

The new type of magnetoelectric effect observed at the domain walls in iron garnet films is considered. This effect manifests itself as a kind of refraction of the stripe domain structure at the charged stripe electrode. The numerical micromagnetic simulation taking into account inhomogeneity of electric field from the stripe electrode as well as magnetic anisotropy of the (210) iron garnet films reproduces the main features of the shape of the domain walls in the vicinity of the electrode edges.

Domain structure ordering and magnetic property enhancement of containerlessly processed quaternary Fe-Mo-Ni-Cr alloy

Quaternary Fe-20 %Mo-12 %Ni-6 %Cr alloy with various composite magnetic structures was fabricated through electromagnetic levitation (EML) coupled with multi-mode quenching techniques. The magnetic domain distributions were characterized and related to the macro/micro-magnetic properties of this containerlessly processed alloy. Under EML condition, nano-scale lamellar (αFe) + Fe2Mo eutectoid structures with completely disordered magnetic domains were formed at small undercoolings. But the eutectoid morphology became anomalous and a ferromagnetic (αFe) single-phase zone with clear stripe domains appeared as undercooling increased, resulting in the obvious improvement of saturation magnetization, coercivity and residual magnetization. The (αFe) + Fe2Mo eutectoid structures were entirely suppressed by multiple quenching processes to secure (αFe) single-phase microstructures with ordered domain distributions including the stripe domains with grain boundary contrast, the maze domains with developed branches and their coexistent mixtures. These magnetic structures displayed much higher saturation magnetization, much lower coercivity and almost unchanged residual magnetization as compared with the highly undercooled alloy at EML state, indicating that the soft magnetic property of this alloy was significantly enhanced after rapid quenching. Moreover, the spin distributions and atomic magnetic moments of two constituent phases were analyzed by first-principle calculations, which were in good accordance with the experimental results.

Hyperfine transition induced by atomic motion above a paraffin-coated magnetic film

We measured transitions between the hyperfine levels of the electronic ground state of potassium-39 atoms (transition frequency: 460 MHz) as the atoms moved through a periodic magneto-static field produced above the magnetic-stripe domains of a magnetic film. The period length of the magnetic field was 3.8 µm. The atoms were incident to the field as an impinging beam with the most probable velocity of 550 m s−1 and experienced a peak oscillating field of 20 mT. Unwanted spin relaxation caused by the collisions of the atoms with the film surface was suppressed by the paraffin coating on the film. We observed increasing hyperfine transition probabilities as the frequency of the field oscillations experienced by the atoms increased from 0 to 140 MHz for the atomic velocity of 550 m s−1, by changing the incident angle of the atomic beam with respect to the stripe domains. Numerical calculation of the time evolution of the hyperfine states revealed that the oscillating magnetic field experienced by the atoms induced the hyperfine transitions, and the main process was not a single-quantum transition but rather multi-quanta transitions.

Compromise Optimized Superior Energy Storage Performance in Lead-Free Antiferroelectrics by Antiferroelectricity Modulation and Nanodomain Engineering.

Lead-free antiferroelectrics with excellent energy storage performance can become the core components of the next-generation advanced pulse power capacitors. However, the low energy storage efficiency caused by the hysteresis of antiferroelectric-ferroelectric transition largely limits their development toward miniaturization, lightweight, and integration. In this work, an ultrahigh recoverable energy storage density of ≈11.4 J cm-3 with a high efficiency of ≈80% can be realized in La-modified Ag0.5 Na0.5 NbO3 antiferroelectric ceramics at an ultrahigh breakdown electric field of ≈67kV mm-1 by the compromise optimization between antiferroelectricity enhancement and nanodomain engineering, resulting in the transformation of large-size ferrielectric antipolar stripe domains into ultrasmall antiferroelectric nanodomains or polarization nanoregions revealing as Moiré fringe structures. In addition, the enhanced transparency with increasing La content can also be clearly observed. This work not only develops new lead-free antiferroelectric energy storage materials with high application potential but also demonstrates that the strategy of compromise optimization between antiferroelectricity modulation and nanodomain engineering is an effective avenue to enhance the energy storage performance of antiferroelectrics.

Subnanosecond Reconfiguration of Ferroelectric Domains in Bismuth Ferrite.

Domain switching is crucial for achieving desired functions in ferroic materials that are used in various applications. Fast control of domains at subnanosecond timescales remains a challenge despite its potential for high-speed operation in random-access memories, photonic, and nanoelectronic devices. In this work, ultrafast laser excitation is shown to transiently melt and reconfigure ferroelectric stripe domains in multiferroic bismuth ferrite on a timescale faster than 100ps. This dynamic behavior is visualized by picosecond- and nanometer-resolved X-ray diffraction measurements as well as time-resolved X-ray diffuse scattering. The disordering of stripe domains is attributed to the screening of depolarization fields by photogenerated carriers resulting in the formation of charged domain walls, as supported by phase field simulations. Furthermore, the recovery of disordered domains exhibits subdiffusive growth on nanosecond timescales, with a nonequilibrium domain velocity reaching up to 10 m/s. These findings present a new approach to image and manipulate ferroelectric domains on subnanosecond timescales, which can be further extended into other photoferroic systems to modulate their electronic, optical, and magnetic properties beyond GHz frequencies. This approach could pave the way for high-speed ferroelectric data storage, computing and photonic applications in a range of photoferroics, and, more broadly, defines new approaches for visualizing the non-equilibrium dynamics of heterogeneous and disordered materials. This article is protected by copyright. All rights reserved.

Current‐Controlled Skyrmion Number in Confined Ferromagnetic Nanostripes

AbstractSkyrmions are vortex‐like localized magnetic structures that possess an integer‐valued topological index known as the skyrmion number or topological charge. Skyrmion number determines the topology‐related emergent magnetism, which is highly desirable for advanced storage and computing devices. In order to achieve device functions, it is necessary to manipulate the skyrmion number in confined nanostructured geometries using electrical methods. Here, the reliable current‐controlled operations for manipulating the skyrmion number through reversible topological transformations between skyrmion chains and stripe domains in confined Fe3Sn2 nanostripes are reported. The results of micromagnetic simulations are successful in numerically reproducing the experiments and explaining them through the combined effect of current‐induced Joule heating and magnetic hysteresis. These findings hold the potential to advance the development of topological spintronic devices.

Field-free room-temperature modulation of magnetic bubble and stripe domains in 2D van der Waals ferromagnetic Fe3GaTe2

Field-free room-temperature modulating magnetic domain structures and realizing stable nanoscale magnetic bubbles in 2D van der Waals (vdW) intrinsic ferromagnets are fundamentally important for 2D spintronic devices. However, it is still very challenging for the absence of a proper room-temperature 2D vdW ferromagnet with suitable perpendicular magnetic anisotropy. Here, by using a 2D vdW intrinsic room-temperature ferromagnetic Fe3GaTe2 crystal with Curie temperature of over ∼340 K and large perpendicular magnetic anisotropy, we study field-free thickness-dependent magnetic domain structure evolution in Au-capped 2D Fe3GaTe2 nanosheets by magnetic force microscopy at room temperature. The magnetic domain varies from a labyrinth-like stripe domain to a single domain in Au/Fe3GaTe2 (20/x nm) with decreasing Fe3GaTe2 thickness from 129 to 17.8 nm. Importantly, the field-free, spontaneous, stable, nanoscale magnetic bubbles can be realized in Au/Fe3GaTe2 (8/x nm) with a wide range of Fe3GaTe2 thickness over 30 nm. The highest bubble density and smallest diameter are measured as ∼2.65 μm−1 and ∼130 nm, respectively, superior to that of most room-temperature magnetic bubble materials. This work paves the way for field-free, room-temperature magnetic domain modulation and vdW-integrated spintronic applications of 2D vdW crystals.

Изучение влияния слабых импульсов магнитного поля на локальные свойства ленточных аморфных сплавов Fe(Ni, Cu)(SiB)

Atomic force microscopy and magnetic force microscopy have been used to study the influence of weak magnetic field pulses on the local properties of ribbon amorphous Fe(Ni, Cu)(SiB) alloys about 100 µm thick, 10 mm wide, and 50 mm long, which were obtained by ultrafast cooling of the melt on a rotating copper drum. On the surface of the tape adjacent to the copper drum, there were practically no areas with low rough-ness, which did not allow subsequent studies of this side of the tape by magnetic force microscopy. This method was used to investigate another, free surface of the foil, which was not adjacent to the copper drum and did not have significant roughness. Prior to the impact of magnetic field pulses on the foil, no magnetic contrast was observed on the free side of the ribbon. After magnetic pulse processing, a magnetic contrast was registered on this side of the foil: stripe domains 0.6–0.8 μm wide became visible, and closing domains, became visible on structural defects, wedge-shaped Neel domains, from 1 µm to 1.6 µm wide. The results of the study allow us to say that the magnetization reversal losses are to a large extent associated with losses due to eddy currents and are associated with the domain width, which depends slightly on the modes of magnetic pulse processing. The obtained results of the research can be used to refine the method for relieving stresses arising in the process of manufacturing amorphous ribbons.

Defect Dipole‐Induced Fatigue Strain Recoverability in Lead‐Free Piezoelectric Ceramics

AbstractPiezoelectric ceramics have garnered extensive utilization in high‐precision actuators, where the magnitude of electric field‐induced strain and fatigue resistance play crucial roles in actuation applications. Herein, an innovative strategy based on defect dipoles is proposed to form a defect‐engineered polymorphic phase transition and achieve a giant piezoelectric strain coefficient of 3080 pm V−1 in Li/Sr‐doped (K0.5Na0.5)NbO3 lead‐free piezoceramics. The mechanism responsible for the enhanced strain performance lies in the optimized strain compatibility between the refined stripe domains and the nanosized domains. Additionally, the results demonstrate that the material is able to recover from fatigue‐induced strain depletion under the stimulation of bipolar electric fields. This property can be phenomenologically explained by the rigid ion model, in which the application of reversal electric fields can facilitate the restoration of defect dipoles, thereby greatly contributing to strain recoverability. This study establishes a close correlation between the unipolar strain properties and the inherent flexibility of defect dipoles and provides new insight into the design of high‐reliability, large‐stroke piezoceramics.

Substrate‐Dependent Anisotropy and Damping in Epitaxial Bismuth Yttrium Iron Garnet Thin Films

AbstractIron garnets that combine robust perpendicular magnetic anisotropy (PMA) with low Gilbert damping are desirable for studies of magnetization dynamics as well as spintronic device development. This paper reports the magnetic properties of low‐damping bismuth‐substituted iron garnet thin films (Bi0.8Y2.2Fe5O12) grown on a series of single‐crystal gallium garnet substrates. The anisotropy is dominated by magnetoelastic and growth‐induced contributions. Both stripe and triangular domains form during field cycling of PMA films, with triangular domains evident in films with higher PMA. Ferromagnetic resonance measurements show damping as low as 1.3 × 10−4 with linewidths of 2.7 to 5.0 mT. The lower bound for the spin‐mixing conductance of BiYIG/Pt bilayers is similar to that of other iron garnet/Pt bilayers.

Structure and stripe domain of melt-spun HoMn6Sn6-xGax ribbons

Topological magnetic skyrmions are expected to become a new generation of information carrier units, and exploring new magnetic skyrmion host materials and their magnetic domain structures is critical. This paper prepared HoMn6Sn6-xGax ribbons by melt-spinning and annealing and studied the effects of the second phase and doping Ga on the structure and magnetic domain of the ribbons. The results show that doped Ga only replaces the Sn sites in the HoMn6Sn6 phase, and the maximum substitution rate of Ga in the HoMn6Sn6 phase is close to 1/6. The unequal substitution of crystal positions causes the lattice to bear considerable compressive stress and negative strain. With an increase in doped Ga content, the lattice constant and cell volume of the HoMn6Sn6-xGax phase gradually decrease, and the substitution positions also change from mainly occupying Sn(2c) sites to occupying Sn(2e) and Sn(2d) sites simultaneously. Doping Ga enhances the preferential orientation in the grains, Ga occupying Sn(2d) sites enhances 〈009〉 orientation, and occupying Sn(2e) sites contributes to the enhancement in 〈204〉 orientation. Whether doped with Ga or not, the ribbons have stable stripe domains with HoMn6Sn6 structure. Increasing Ga content from x = 0.3 to x = 1.6 decreases the spin reorientation temperature, Curie temperatures, and the difference between the two temperatures.