Stripe Domain Structure Research Articles

Fracture behaviors and crack propagation anisotropy in multi-ions modified bismuth titanate ferroelectrics

Bismuth titanate (BIT) is widely considered a promising lead-free piezoelectric material for advanced high-temperature applications. Despite significant advances in high-performance BIT ferroelectrics, there remains little understanding of mechanical properties including fracture failure and crack propagation behaviors, hindering the optimization of stability and reliability for next-generation high-temperature ferroelectrics. In this work, we investigated mechanical fracture and crack propagation behaviors of a type of high-performance bismuth titanate-based ceramic (Bi3.96Ce0.04Ti3–2xWxNbxO12, BCTWN) with different doping contents and electric poling states. High-resolution transmission electron microscopy (HRTEM) and electron backscatter diffraction (EBSD) results reveal that the BCTWN ceramics possess a single ferroelectric phase and exhibit layered crystal structures characterized by periodic fringe features. In addition, the striped domain structures are observed on the surface of plate-like grains. Mechanical measurements indicate that fracture behaviors of BCTWN ceramics are significantly affected by doping contents. The ceramics with the largest grain size present inferior microstructure with more defects, endowing the lowest bending strength and fracture toughness. For the samples with different poling states, strong anisotropy in crack propagation and fracture toughness is observed, attributed to the different domain switching mechanisms driven by local incompatible stress fields, which is experimentally validated by the intriguing evolutions of striped domain structures around crack tips. This work advances our understanding of the fracture and crack propagation mechanisms of BIT-based ceramics and provides insight into tailoring the mechanical behaviors through doping and poling strategies.

Analysis of Relationship between Microwave Magnetic Properties and Magnetic Structure of Permalloy Films

Changes in the microwave permeability of permalloy films with an increase in the film thickness are studied. Measurement data on the evolution of microwave permeability with film thickness are analyzed in the framework of a model for the film with a regular stripe domain structure and out-of-plane magnetic anisotropy. A correlation between the microwave magnetic properties and magnetic structure of permalloy films is established. It is demonstrated that the observed decrease in the ferromagnetic resonance frequency and the static permeability with a growth in the film thickness can ascribed to the appearance of perpendicular anisotropy and the formation of a stripe domain structure. The calculated dependences of the ferromagnetic resonance frequency and static permeability on the film thickness are in reasonable agreement with the measurement results. Based on the analysis of these dependences, the domain width in the permalloy films is estimated. It is found that for thick permalloy films, the domain width is of the order of the film thickness. The results obtained may be useful for high-frequency applications of soft magnetic films.

Investigation of transverse exchange-springs in electrodeposited nano-heterostructured films through first-order reversal curve analysis

The prerequisite of efficient exchange-spring nano-heterostructures, i.e., tuning both hard and soft phases at a nanometer level, has posed significant preparation challenges to ensure effective exchange-coupling. Here, we present a novel approach to fabricate transverse exchange-spring nano-heterostructures using single starting material through an “in situ” electrodeposition technique at room temperature. Utilizing modified acidic bath chemistry and controlled hydrogen evolution, we successfully prepared stress-free, shiny, fine-grained amorphous, and nanocrystalline Co-rich cobalt phosphorus films. These nano-heterostructured films exhibit a unique non-collinear anisotropy-driven transverse exchange-spring behavior, investigated systematically under ambient conditions. The comprehensive functional analyses reveal that intricate interplay between in-plane (IP) anisotropy of amorphous phase and out-of-plane (OOP) anisotropy generating from a nanocrystalline structure compete with each other, while producing characteristic stripe domain structures to novel corrugated stripe domain shapes. The angle-dependent first-order reversal curve distributions demonstrate new insights into the magnetic reversal mechanisms, further confirming the non-exchange-spring and exchange-spring nature of the films depending on the prevalent interfacial exchange coupling. Formation of anisotropy-driven metastable-state due to competition between IP and OOP anisotropy at a particular OOP orientation has led the normal exchange-spring structures to a transverse exchange-spring structure. Micromagnetic simulations, in excellent agreement with experimental data, further elucidate the formation of characteristic stripe domain patterns and the influence of anisotropy on the magnetic properties. The innovative methodology and detailed functional analysis presented here offer significant understanding to the field of exchange-spring magnetic materials, including anisotropy-driven metastable states, demonstrating the potential for scalable and cost-effective fabrication of advanced nano-heterostructures with tailored magnetic properties.

Self-assembled growth of stripe nanodomains induced by single-pulse: IR laser irradiation in LT crystals covered by conductive layer

In this work we have studied the stripe domain structure created by single pulse IR laser irradiation in CLT crystals covered by a conductive layer. The formation of three types of domain patterns was distinguished: (1) the central region with curved stripe domains, (2) the middle region with straight rays and branches oriented in three directions, and (3) the wide edge region covered by parallel straight rays oriented in only one direction. The obtained results have been considered as domain growth in highly-nonequilibrium switching conditions under the action of spatially nonuniform pyroelectric field arising during cooling after pulse laser irradiation.

Growth of submicron domain structures in electric field at elevated temperatures in lithium niobate with surface dielectric layer

The formation of submicron stripe domain structures was studied during two-stage switching with a change in the dimensionality of domain growth in congruent lithium niobate with a dielectric layer on the polar surface at elevated temperature. At the first stage, a two-dimensional hexagonal microdomain lattice representing a structure of isolated domains was created using the photoresist mask. After that, the polar surface was covered by solid dielectric layer. Thus, switching at the second stage was carried out under inefficient screening of depolarization field leading to growth of the stripe domains only. Self-organized formation of domain stars and snowflakes was demonstrated.

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.

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.

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.

Li0.5Bi2.5Nb2O9: An alkali‐metal bismuth layer structured ferroelectric with high TC and small orthorhombic distortion

AbstractBismuth layer structured ferroelectrics (BLSFs) have drawn much attention due to their great potential for high‐temperature applications. It is generally accepted that BLSFs with small orthorhombic distortion should have low TC. In this paper, we report an anomalous example Li0.5Bi2.5Nb2O9 (LBN), which has small orthorhombic distortion but very high TC. LBN shows the highest TC (834°C) among currently reported prototype alkali‐metal BLSFs, which is attributed to its small tolerance factor. However, the refinement result reveals that LBN is orthorhombic with the space group of A21am, and the orthorhombic distortion of LBN a/b is merely 1.0019. The measurement of piezoelectric coefficient (d33 ∼ 6 pC/N) and observation of striped domain structure confirm the ferroelectricity nature of LBN. This work deepens our understanding of BLSFs and may lead to the finding of more novel BLSFs with high performance.

Rotatable anisotropy in exchange bias bilayer and stripe domains films with uniaxial anisotropy

We report the rotatable anisotropy in three magnetic film systems, including in-plane magnetized FeNi film, FeNi/FeMn bilayer and FeNi stripe domains (SDs) structure film. Omnidirectional ferromagnetic resonance driven by rotatable anisotropy can be achieved in these films. We have found that the in-plane magnetized FeNi films have a negligible rotatable anisotropy of about 1 ∼ 2 Oe. Rotatable anisotropy fields of 6.1 Oe and 5.5 Oe are found for isotropic and anisotropic FeNi/FeMn bilayers, which comes from the exchange coupling at the interface of FM and AFM layer. This magnitude is smaller than the value found in thick FeNi film where a big rotatable anisotropy field of 87 Oe is present stemming from its domain structure. In addition, the uniaxial anisotropy could tailor the resonance frequency from 0.78 and 2.28 GHz for in-plane magnetized FeNi thin film, and 1.3 to 2.4 GHz for FeNi SDs films. Furthermore, a conclusion that a uniaxial anisotropy has no influence on rotatable anisotropy in three magnetic films systems, was yielded.

Performance Enhancement of a Spin-Wave-Based Reservoir Computing System Utilizing Different Physical Conditions

We numerically study how to enhance reservoir computing performance by thoroughly extracting the spin-wave device potential for higher-dimensional information generation. The reservoir device has a 1-input exciter and 120-output detectors on the top of a continuous magnetic garnet film for spin-wave transmission. For various nonlinear and fading-memory dynamic phenomena distributing in the film space, small in-plane magnetic fields are used to prepare stripe domain structures and various damping constants at the film sides and bottom are explored. The ferromagnetic resonant frequency and relaxation time of spin precession clearly characterizes the change in spin dynamics with the magnetic field and damping constant. The common input signal for reservoir computing is a 1-GHz cosine wave with random 6-valued amplitude modulation. A basic 120-dimensional reservoir output vector is obtained from time-series signals at the 120-output detectors under each of three magnetic field conditions. Then, 240- and 360-dimensional reservoir output vectors are also constructed by concatenating two and three basic ones, respectively. In nonlinear autoregressive moving average (NARMA) prediction tasks, the computational performance is enhanced as the dimension of the reservoir output vector becomes higher and a significantly low prediction error is achieved for the tenth-order NARMA task using the 360-dimensional vector and optimum damping constant. The results are clear evidence that the collection of diverse output signals efficiently increases the dimensionality of the integrated reservoir state vector (i.e. reservoir-state richness) and thereby contributes to high computational performance. This paper demonstrates that performance enhancement through various configuration settings is a practical approach for on-chip reservoir computing devices with small numbers of real output nodes.

Physical properties of Cr-doped epitaxial BiFeO3 thin films influenced by ferroelectric domain structures

We investigated the physical properties of Cr-doped epitaxial BiFeO3 (CBFO) thin films influenced by ferroelectric domain structures. The epitaxial CBFO thin films with Cr concentrations of 0, 2, 4, 6, and 8% were deposited on Nb-doped single crystal SrTiO3 substrates by pulsed laser deposition. The epitaxial CBFO thin films with Cr concentrations of 0, 2, and 4% had highly c-oriented crystallinity and the epitaxial CBFO thin films with Cr concentrations of 6% and 8% exhibited mixed crystallinity of c-oriented crystallinity and (101)-oriented crystallinity. The CBFO thin film with a Cr concentration of 4% showed the highest ferroelectric polarization, and the ferroelectric polarizations of the CBFO thin films with a Cr concentration of more than 4% were reduced by the formation of (101)-oriented grains. On the other hand, the piezoelectric properties, leakage current characteristics, and ferromagnetic properties of CBFO thin films were simultaneously improved by increasing the Cr concentration. Terraces indicating layer-by-layer growth were observed on the surface of the CBFO thin films, and the edges of the terraces formed on the surface of the CBFO thin films were blurred when the Cr concentration increased. The ferroelectric domain structures of the CBFO thin films observed with a piezoelectric response microscope changed from a stripe domain structure to a mosaic domain structure when the Cr concentration exceeded 6%.

Imaging and control of periodic array of stripe domain and domain wall in epitaxial BiFeO3 thin films

Ferroelectric stripe domain structure and domain walls were investigated by vector PFM on epitaxial BiFeO3 thin films. Measurements of topography of film versus distance between spikes, we identify the [Formula: see text] domain in the film, were supported by XRD and AFM characterization. [Formula: see text] domain can be switched under the electric field engendered by the biased PFM tip, and their controllable [Formula: see text] rotation can be maintained by electron injection by the PFM tip. These stripe domain walls are conductive, provide an opportunity to further study their new properties in high-density memory devices.

Seeding and Emergence of Composite Skyrmions in a van der Waals Magnet.

Topological charge plays a significant role in a range of physical systems. In particular, observations of real-space topological objects in magnetic materials have been largely limited to skyrmions - states with a unitary topological charge. Recently, more exotic states with varying topology, such as antiskyrmions, merons, or bimerons and 3D states such as skyrmion strings, chiral bobbers, and hopfions, have been experimentally reported. Along these lines, the realization of states with higher-order topology has the potential to open new avenues of research in topological magnetism and its spintronic applications. Here, real-space imaging of such spin textures, including skyrmion, skyrmionium, skyrmion bag, and skyrmion sack states, observed in exfoliated flakes of the van der Waals magnet Fe3-x GeTe2 (FGT) is reported. These composite skyrmions may emerge from seeded, loop-like states condensed into the stripe domain structure, demonstrating the possibility to realize spin textures with arbitrary integer topological charge within exfoliated flakes of 2D magnets. The general nature of the formation mechanism motivates the search for composite skyrmion states in both well-known and new magnetic materials, which may yet reveal an even richer spectrum of higher-order topologicalobjects.

Directional growth effect on magneto-mechanical properties of Fe81Al19 alloy

Directional growth effect on magneto-mechanical properties of Fe81Al19 alloy is studied. The ideal model of heat flux for directional solidification (DS) technique is proposed, and the tuned A/L (the ratio of cross-sectional area and length for the ingot) and ΔT (temperature difference) are adopted to increase heat flux (q). The experimental result shows that the increase of q effectively promotes the degree of (011)[100] Goss texture and therefore helps to form an oriented stripe domain structure. Large λ100 of 93.8 ppm attained for this optimized Fe81Al19 alloy prepared by DS method is very close to that of the Fe81Al19 single crystal (95.0 ppm). For the optimized DS prepared Fe81Al19 alloy, high magnetostriction sensitivity (dλ/dH) of 0.45 ppm/Oe leads to huge ΔEs/E0 of ∼10% and attractive ΔE/E0 of 8.2% at small H = 0.25 kOe. The above remarkable magneto-mechanical properties, low cost of Fe81Al19, and simple process of DS favor for applications. This work proposes an ideal model to emphasize the importance of heat flux in DS, and experimentally attains the remarkable magneto-mechanical properties for Fe81Al19 alloy prepared by DS.

Генерация ЭДС магнитостатическими волнами в структуре ЖИГ(111)-Pt в слабых полях подмагничивания

In a structure of an epitaxial film of yttrium iron garnet (YIG) with crystallographic orientation (111) 11.8 μm thick and a 5 nm thick platinum (Pt) film deposited on its surface, the effect of EMF generation in a platinum film during the propagation of magnetostatic waves (MSW) in the structure was studied at values of the tangential constant magnetic field H less than the saturation field H_s~65 Oe of the YIG film. The experiments were performed in a geometry where the field H was parallel to the crystallographic direction [1¯21] and to the MSW antennas, and the distances from the input antenna to the output antenna and to the Pt film were ~5 mm and ~0.5 mm, respectively. In the structure under consideration, at |H|<H_s, a stripe domain structure (SDS) was formed, which in fields |H|<H_1~5 – 7 Oe acquired a branching character in the near-surface layer. In the range of fields H_1<|H|<H_2≈40 Oe, MSW propagation was observed in the frequency band ∆F_1~ 300-550 MHz, which was accompanied by EMF generation due to the inverse spin Hall effect. In the interval H_2<|H|≤H_s, MSW propagation was observed in the frequency band ∆F_2≈ 750-1750 MHz, while the frequency interval in which the EMF signal was recorded turned out to be several times smaller due to the development of MSW parametric instability.

Magnetization enhanced the multiple magnetic domain-dominated resonance modes in stripe domain films

FeCoHf films with different Hf contents and thicknesses were deposited by composition-gradient sputtering. The results showed that the stripe domain (SD) structure emerges when the film thickness exceeds a critical thickness (220–330 nm), but the increase in introduced Hf leads to a decrease in magnetization, and in turn, the stripe phase weakens and eventually disappears. Dynamic measurements revealed magnetic domain-dependent resonant absorption spectra with up to seven resonance peaks, which have rarely been observed in magnetic film with an established SD structure. The number of resonant peaks can be controlled by the saturation magnetization of the film. Micromagnetic simulations indicate that multiple magnetic domain resonance modes can be attributed to the enhanced magnetization, which induces an increase in the magnetic domain wall volume. These results emphasize the pivotal role of magnetic domain dynamics in the framework of spintronic and microwave devices.

Tuning rotational magnetization for high frequency magnetoimpedance in micro-patterned triangle spiral magnetic systems

Achieving high sensitivity, resolution, and accuracy is desirable and in high demand for magnetic sensor applications. The giant magnetoimpedance (GMI) effect has drawn intensive attention owing to its ultrasensitive response to the magnetic field. Further enhancement of the GMI effect in soft magnetic conductors (wires, ribbons, or films) is essential but represents a big challenge since the experimentally reported highest GMI ratio is still much smaller than its theoretically predicted value. Inspired by the kirigami structures, we propose a new approach for improving the GMI effect by designing triangle spiral magnetic systems. We demonstrate that the GMI ratio can be easily tuned by varying the edge width of the triangle spiral magnetic ribbon. The GMI ratio is enhanced up to 250% and 100% for the Fe 92.5 C 3.5 Si 3.9 ribbon with a 60 μm wide edge when a magnetic field of 100 Oe is aligned along the altitude and edge directions, respectively. Magnetometry indicates that upon reduction of the edge width, the improvement of magnetic susceptibility at low applied fields is correlated with the strengthened shape anisotropy. Micromagnetic simulations suggest that various closure magnetic domain configurations such as stripe and zig-zag domain structures can be formed, depending on the applied magnetic field directions, as a result of the competition of anisotropy and Zeeman energies followed in the Stoner-Wohlfarth model. The simulated results fully support the experimentally observed GMI enhancement and attribute it to the formation of transverse magnetic domains at the critical dimension of the micro-patterned magnetic ribbon system. These superior properties make the triangle-spiral GMI sensor a promising candidate for advanced sensor applications. • Various branch-width triangle spiral magnetic systems have been developed and characterized, at which optimized 60 μm width showing the best GMI effect owing to the strengthened shape anisotropy. • The GMI effect is augmented up to 250% and 100% under an applied magnetic field of 100 Oe aligned along with the altitude and edge directions, respectively. • The GMI enhancement is supported by transverse domain formations approved by OOMMF micromagnetic simulation. • Wide range of magnetic domain configurations can be formed depending on the applied magnetic field directions, originating from the competition of anisotropy and Zeeman energies followed in the Stoner-Wohlfarth model.

Boosting the Photocurrent in BiFeO3 Thin Films via a Domain‐Wall‐Defect Interaction

Ferroelectric domain walls are of great interest due to their nontrivial electronic properties. Herein, a large photocurrent is detected only in the stripe domain structure of BiFeO3 thin films. By the temperature‐resolved time‐dependent photocurrent measurements, the significant trapping effect is revealed to be associated with the abnormal photocurrent. Further optoelectronic measurements with the defect density tuned unveiled that the interaction between the defects and domain walls is essential to give a rise to a large photocurrent in BiFeO3 thin films. The study reveals a novel domain‐wall‐defect photovoltaic effect and provides a simple thermal annealing‐treatment strategy to boost the photocurrents and power output by several folds.

Magnetization statics and dynamics in (Ir/Co/Pt)6 multilayers with Dzyaloshinskii–Moriya interaction

Magnetic multilayers of (Ir/Co/Pt)6 with interfacial Dzyaloshinskii-Moriya interaction (IDMI) were deposited by magnetron sputtering with Co thickness d=1.8 nm. Exploiting magneto-optical Kerr effect in longitudinal mode microscopy, magnetic force microscopy, and vibrating sample magnetometry, the magnetic field-driven evolution of domain structures and magnetization hysteresis loops have been studied. The existence of weak stripe domains structure was deduced – tens micrometers size domains with in-plane “core” magnetization modulated by hundred of nanometers domains with out-of-plane magnetization. Micromagnetic simulations interpreted such magnetization distribution. Quantitative evaluation of IDMI was carried out using Brillouin light scattering (BLS) spectroscopy as the difference between Stokes and anti-Stokes peak frequencies Δf. Due to the additive nature of IDMI, the asymmetric combination of Ir and Pt covers led to large values of effective IDMI energy density Deff. It was found that Stokes and anti-Stokes frequencies as well as Δf, measured as a function of in-plane applied magnetic field, show hysteresis. These results are explained under the consideration of the influence of IDMI on the dynamics of the in-plane magnetized “core” with weak stripe domains.