Domain Width Research Articles

Thermally assisted fabrication of nonlinear photonic structures in lithium niobate with femtosecond laser pulses

Engineered domain structures play an essential role in nonlinear optics for quasi-phase-matched parametric processes. Pyroelectric field-assisted domain inversion with focused femtosecond laser pulses is a promising approach to create arbitrary two-dimensional nonlinear photonic structures in a large volume without externally applied electrical fields. We fabricate lattices of ferroelectric domains by patterning lithium niobate crystals with femtosecond laser pulses and then heating them to elevated temperatures. After cooling to room temperature, domains form below and above the laser-induced seeds. We investigate the effect of temperature and seed spacing on the number and size of inverted domains. In a temperature range of 220 °C-300 °C all domains are inverted in a two-dimensional lattice with periods of 15 µm × 6.3 µm. Smaller lattice periods result in a smaller fraction of inverted domains. Measurements with conducting, nonconducting, and short-circuited crystal surfaces reveal the influence of surface charges during the domain formation process. From the obtained domain widths and spacings, we calculate the effective nonlinear coefficient of quasi-phase-matched second-harmonic generation in two-dimensional nonlinear photonic structures.

Continuously tunable ferroelectric domain width down to the single-atomic limit in bismuth tellurite

Emerging functionalities in two-dimensional materials, such as ferromagnetism, superconductivity and ferroelectricity, open new avenues for promising nanoelectronic applications. Here, we report the discovery of intrinsic in-plane room-temperature ferroelectricity in two-dimensional Bi2TeO5 grown by chemical vapor deposition, where spontaneous polarization originates from Bi column displacements. We found an intercalated buffer layer consist of mixed Bi/Te column as 180° domain wall which enables facile polarized domain engineering, including continuously tunable domain width by pinning different concentration of buffer layers, and even ferroelectric-antiferroelectric phase transition when the polarization unit is pinned down to single atomic column. More interestingly, the intercalated Bi/Te buffer layer can interconvert to polarized Bi columns which end up with series terraced domain walls and unusual fan-shaped ferroelectric domain. The buffer layer induced size and shape tunable ferroelectric domain in two-dimensional Bi2TeO5 offer insights into the manipulation of functionalities in van der Waals materials for future nanoelectronics.

Об интервальном оценивании с высоким порядком минимума функции

The article addresses the problem of two-sided estimation of the minimum of a function of one real variable using interval methods. These methods are widely used for finding the ranges of functions, but their order of accuracy often does not exceed 3 for the functions of one variable and 2 for the case of many variables. The paper proposes a method for finding an interval estimate for the minimum of a function of one variable with any odd order greater than 2. The proposed technique uses so-called functional intervals, the boundaries of which are described by polynomials of even degrees obtained from the Taylor formula for the function under consideration. The article provides a derivation of interval estimates for the minimum, and also proves an estimate for the order of convergence of the width of the resulting interval with the decrease in the size of the domain of the function. An example is given in which estimating the minimum of a function reaches the theoretical order of convergence. The approach developed in this paper allows, in principle, to achieve any odd accuracy order in the interval estimation of the minimum of a function. In practice, this method is convenient to use for the third order of accuracy, since, on the one hand, we need to find an interval estimate for derivatives of high degrees, and, on the other hand, we need to find roots of polynomials of even degrees. The new approach is shown to be useful and practical, as it uses the local Taylor expansion and therefore behaves stably as the width of the function domain decreases. The new approach can be used to improve the performance of interval global optimization algorithms based on adaptive domain partitioning. An increase in the order of estimation accuracy entails the acceleration of these algorithms, as well as a decrease in the number of subintervals generated in the process of partitioning the domain.

Deciphering the individual effects of the fluid flow and material evaporation physics on the melting characteristics and the re-solidification parameters during laser melting of solid Ti6Al4V substrate

• Underlined individual effects of fluid flow and material evaporation separately. • Effect of adding various physics on the computational time consumption presented. • Four different models have been investigated for laser melting of Ti6Al4V. • Optimal numerical model for laser melting has been identified. • Detailed discussion on the solidification parameters in melt pool presented. In this study, the effect of inclusion of fluid flow and material evaporation physics in the thermal models of the laser melting process for Ti6Al4V has been compared to evaluate their individual influence on the simulation results and computational resources consumed. Though the study seems basic, it aims to address the important issue of increase in the computational resources consumption and time when these physics are added to the model. The study also focuses upon finding an optimized model that can enable faster prediction of thermal and melt pool dimension results for macro-scale laser melting cases, while ensuring the accuracy of these results against the experimental observations. It was seen that the fluid flow and material evaporation assisted each other in some aspects and opposed in some others, but the extent of their individual effects varied significantly in the magnitudes. Along with the individual melt pool characteristics comparison, the thermal field along the length, width and depth of the computational domain as well as the computational time consumed by each simulation are also compared for different models. It is obtained through experimental validation that material evaporation could reduce the reliance on the fluid flow inclusion in the model to accurately predict the melt pool dimensions, that too while consuming drastically less computational time. Through these comparisons and experimental validation, an optimized model has been identified, which is then used to present a parametric analysis of the solidification variables (G, R, GR and G/R) for the laser melting of Ti6Al4V.

Magneto-optical diffractive deep neural network.

We propose a magneto-optical diffractive deep neural network (MO-D2NN). We simulated several MO-D2NNs, each of which consists of five hidden layers made of a magnetic material that contains 100 × 100 magnetic domains with a domain width of 1 µm and an interlayer distance of 0.7 mm. The networks demonstrate a classification accuracy of > 90% for the MNIST dataset when light intensity is used as the classification measure. Moreover, an accuracy of > 80% is obtained even for a small Faraday rotation angle of π/100 rad when the angle of polarization is used as the classification measure. The MO-D2NN allows the hidden layers to be rewritten, which is not possible with previous implementations of D2NNs.

Magneto-mechanical and damping properties in Fe79.9Al20-xGaxTb0.1 alloys

Large magneto-mechanical properties are attained for Fe79.9Al20−xTb0.1Gax alloys prepared by directional solidification (DS). We obtain high delta E (ΔE) effect of 9.1–13.4 % and magneto-mechanical coefficient (K) of 29.7–49.5 % with good controllability of E by H and high sensitivity of E at low H, beneficial for the practical applications. The enhanced ΔE effect and K is sensitive to Ga content mainly due to the increased magnetostriction susceptibility (dλ///dH). The improved dλ///dH is contributed from the increased Δλ mainly due to lattice softening with Ga substitution for Al in A2 phase and also magnetic softening, possibly associated with higher (110) texture. The almost linear relationship between ΔEs/E0 and K2 suggests the experimental ΔEs/E0 obtained from IEV-RFDA (f ∼ 2 kHz) well agrees the theoretical estimated K2 according to the sound propagation theory. Besides, Ga substitution decreases damping capacity of the alloys Ψ(=ΔW/W), the change of the damping capacity (ΔΨ) with H, from 3.73 % for x = 0–0.73–1.04 % for x = 5–20. The almost linear relation between the experimental ΔΨ and theoretically estimated Ψeth reveals the micro eddy-current mechanism dominates the ΔΨ at 2 kHz. The decreased in ΔΨ, measured by RFDA with Ga substitution is mainly related to the reduction of the magnetic domain width and the decrease of E0 due to lattice softening. Several anelastic effects are reported for sub-resonance forced vibrations (DMA: 0.1–30 Hz): thermally activated Snoek (P1) and Zener (P2) effects and high damping plateau (background Qb−1) below 200 °C even for low strain (5 ×10−3 %). Dependence of the background damping level (Qb−1) on ratio Al/Ga is also non-linear with the maximum in ternary compositions Fe-20(Al+Ga).

Rigorous single-period micromagnetic model of stripe domains: Comparison with analytics and experiment

Stripe domains in thin films form through a complex competition of perpendicular anisotropy and demagnetizing energy and are still lacking a complete micromagnetic description, despite being investigated since 50 years. This paper elucidates the formation of stripe domains with a special focus on the dependence of stripe domain width on film thickness with varying ratio of the two major energy contributions. An overview and review of the most established analytical models for the calculation of this dependency is given with respect to experimental data. For this purpose, new measurements on epitaxial Fe-Co-C films with perpendicular anisotropy have been performed. An efficient and rigorous micromagnetic simulations method is proposed, which proved to be comparable or better than previous models in describing experimental findings, especially for films with strongly dominating demagnetizing energy. Comprehensive simulations were performed to determine thickness-dependent stripe width for various material parameters, which can serve as a benchmark for analytical theories or can be used directly for comparison with experimental results. At a given combination of exchange constant and saturation polarization there exists a specific thickness at which the stripe width is independent of the uniaxial anisotropy.

Influence of ion structure and solvent electric dipole on ultrananoporous supercapacitor: a lattice model study

A five-state modified BEG model is proposed for describing electrolyte in polar solvent in cylindrical electrode pore in which only one row of particles can be stationed. Two properties the closest to the actual situation of the aqueous electrolyte are integrated into the model: cation is dimer comprised of two tangentially tethered hard spheres of different diameters: one is charged, while the other is neutral, and polar solvent is modeled as neutral hard sphere with an electric dipole. The system partition function is obtained by numerically solving maximum real root of characteristic equation of Kramers-Wannier transfer matrix. The model is used to investigate effects of ion structure and electric valence, solvent electric dipole, and cylindrical pore radius on specific differential capacitance and specific energy storage of the resulting supercapacitor. Main findings are briefly described below. (i) The dimer counter-ion electric valence does not exert obvious influence on the saturation value of the but reduces the threshold electrode potential strength beyond which the value is just reached. (ii) Whether the dimer counter-ion is monovalent or bivalent, the peak height and the value tend to rise with the dimer neutral site size decreasing, but influence of the value on the value is very small. Only when the value is small enough, the value rises a little with decrease of the value. (iii) Increase of solvent electric dipole moment (whether by increasing the dipole charge or dipole length) always raises the value, and enlarges width of the pure solvent domain or zero and zero domain around the zero electrode potential, but does not change the value obviously. (iv) With the pore size increasing, the value reduces and the value increases. So, using small size pore is favorable to improve the supercapacitor performance from the perspective of energy storage and electrode potential applied. (v) The three parameters: dipole charge, and dipole length, are cooperative in influencing the value.

Effective electrostatic forces between two neutral surfaces with surface charge separation: valence asymmetry and dielectric constant heterogeneity

Based on CDFT calculations, we study new features of surface electrostatic force (SEF) between two face-to-face overall neutral surfaces, each of which is comprised of atomic scale strip shape charge distribution and is immersed in +2:−1 electrolyte. Dielectric constant of near surface fluid is lower than that of distant fluid. Ion valence and dielectric constant heterogeneity effects are reflected in the following aspects. (i) For asymmetrical configuration of the strip shape charge distribution, if the coexistence bulk mole concentration is high like , one repulsion peak of the SEF appears at approximately two times the ion diameter and the peak height increases obviously with the ion valence and the strip shape domain width ; however, for low value, like , the ion valence almost does not cause any effect on the SEF shape and strength at small distances except that the higher valence ion causes a higher decaying rate of the SEF with the surface separation. (ii) For the case of the asymmetrical configuration and bivalent ion, strength of the small distance attractive SEF always reduces with the value, and is positively correlated with the value except when the value is high and the domain surface charge strength is low. (iii) The symmetrical strip shape charge distribution is an efficient way in inducing the attractive SEF in presence of bivalence ions even if the value is low down to ; the attraction strength is positively correlated with the value. (iv) The ion adsorption, playing a key role in influencing the SEF for the present overall neutral two-surface system, generally increases with the value, and far higher than that relevant to two similarly charged surfaces with equal value. (v) The lower surface fluid dielectric constant accords both the force and potential curves with new features like alternative mode of attraction and repulsion even in low bulk concentration, big strength in comparison with the average thermal energy, and large insensitivity to the surface charge distribution patterns and ion valence.

Studies on tunable simultaneous RGB generation in domain engineered magnesium oxide doped periodically poled lithium niobate structures

Simultaneous generation of red (R), green (G), and blue (B) wavelengths in different grating structures of 5% MgO doped domain engineered LiNbO3 is studied theoretically by employing the type-0 quasiphase-matched (QPM) technique. The spectral output from two cascaded, four segmented, and two-phase shifter (PS) QPM structures using second-harmonic generation, difference-frequency generation, sum-frequency generation, and third harmonic generation were analyzed and interpreted. We observed RGB in the range of 620 to 650 nm, 530 to 580 nm, and 430 to 468 nm for red, green, and blue, respectively, for various configurations of input wavelength, period, device length, segment length, location, and width of the PS domain. The influence of the input pump, operating temperature, pump detuning, PS width, and phase matching periods are analyzed for all the proposed schemes. Fluctuation in the output wavelengths of about 10 to 20 nm was observed due to the temperature variations from 25°C to 150°C in steps of 25°C. Further, the advantages of using a MgO-PS QPM structure over the other proposed schemes have also been addressed for their potential application in a laser-based projection display system.

Effect of Humidity on the Writing Speed and Domain Wall Dynamics of Ferroelectric Domains (Adv. Electron. Mater. 6/2022)

Ferroelectric Thin Film-Based Memories In article number 2100650, Gustau Catalan, Neus Domingo, and co-workers demonstrate that the maximum speed at which ferroelectric thin film-based memories can be written accelerates with atmospheric humidity – and, conversely, slows down in dry conditions. The domain width as a function of relative humidity follows the behavior of the water adsorption isotherm, revealing the interplay between water layer thickness and screening. Image by Damaso Torres, ICN2.

Decay of domains created by local switching on non-polar cut of MgO doped LiNbO3 single crystals

Decay of isolated wedge-like domains with charged domain walls during local switching by a biased SPM tip on non-polar cut of lithium niobate doped by MgO was studied using piezoresponse force microscopy. It was found that domain imaging led to domains length reduction, whereas domain width did not change. Domain decay without scanning was also revealed. All the obtained effects were attributed to influence of injected charges, residual depolarization field, and AC voltage. Spatial distribution of electric field near SPM tip was simulated numerically. The obtained results provide new understanding of domain decay problem for nanodomain engineering.

Effect of thickness and frequency of applied field on the switching dynamics of multiferroic bismuth ferrite thin films

Epitaxial films of multiferroic $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ (BFO) with different thicknesses are grown on $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$ buffered $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ (001) substrates using the pulsed laser deposition technique. The room-temperature polarization-voltage (P-V) hysteresis loop, leakage current and average domain size of films with varying thicknesses have been investigated. The frequency dependence of the coercive voltage and variation of the coercive voltage as a function of film thickness are ascertained to examine the validity of the Ishibashi-Orihara model and the semi-empirical Kay-Dunn scaling relationship, respectively. The results demonstrate that at room temperature the BFO films indeed follow the Ishibashi-Orihara (I-O) model and Kay-Dunn scaling law. The dimensionality of the domains acquired by piezoresponse force microscopy imaging further validates that found from the I-O model scaling exponent and is consistent with Kittel's law regarding dependence of domain width on film thickness. These combined results elucidate the fundamental properties that govern the switching kinetics of BFO and are relevant for BFO-based multiferroic materials in next generation logic and memory devices operating over a wide range of frequencies.

Influence of Varying Tensile Stress on Domain Motion.

Magnetic domain motion has been widely studied in the fields of spintronics, nanowires, and thin films. However, there is a lack of such studies on industrial steels, especially for domain motion under the action of varying stress. Understanding domain motion under stress is helpful for the improvement of evaluation accuracy and the establishment of theoretical models of passive, nondestructive testing technology. This paper presents the influence of varying tensile stresses on the magnetic domain motion of silicon steel sheets. Magnetic domain rotation and domain wall displacement were characterized using magnetic domain images, and their motion mechanisms under elastic and plastic stresses are presented. The results show that the domain rotation under stress involves reversible and irreversible changes. The effect of material rearrangement on domain rotation and domain wall displacement after plastic deformation is discussed. Based on the motion mechanism, a threshold stress value (TSV) required for the complete disappearance of the supplementary domains in the elastic range is proposed, enabling the classification of the elastic stress ranges in which the reversible and irreversible domain rotations occur. In addition, the effect of microstructure on TSV is also discussed, and the results show that the regions far away from the grain boundary need larger stresses to complete an irreversible domain rotation. Additionally, the domain width and orientation also affect the TSV. These findings regarding the domain motion mechanism and TSV can help to explain the sequence of domain rotation under stress and modify the stress assessment under dynamic loads in electromagnetic nondestructive evaluation, especially in the magnetic memory method.

Advanced Characterization of FeNi-Based Films for the Development of Magnetic Field Sensors with Tailored Functional Parameters.

Magnetometry and ferromagnetic resonance are used to quantitatively study magnetic anisotropy with an easy axis both in the film plane and perpendicular to it. In the study of single-layer and multilayer permalloy films, it is demonstrated that these methods make it possible not only to investigate the average field of perpendicular and in-plane anisotropy, but also to characterize their inhomogeneity. It is shown that the quantitative data from direct integral and local measurements of magnetic anisotropy are consistent with the direct and indirect estimates based on processing of the magnetization curves. The possibility of estimating the perpendicular magnetic anisotropy constant from the width of stripe domains in a film in the transcritical state is demonstrated. The average in-plane magnetic anisotropy field of permalloy films prepared by magnetron sputtering onto a Corning glass is almost unchanged with the thickness of a single-layer film. The inhomogeneity of the perpendicular anisotropy field for a 500 nm film is greater than that for a 100 nm film, and for a multilayer film with a total permalloy thickness of 500 nm, it is greater than that for a homogeneous film of the same thickness.

On the Rate Dependence of Precipitate Formation and Dissolution in a Nickel-Base Superalloy

The temporal dependence of gamma ' dissolution in the polycrystalline Ni-base superalloy RR1000 has been studied with implications to thermo-mechanical processing. A resistivity-based method using an electro-thermal mechanical testing (ETMT), which overcomes the drawbacks associated with other approaches, such as calorimetry, dilatometry, and diffraction, has been used to explore the effect of transient and isothermal thermal cycles. This is supplemented by DICTRA numerical models that simulate the diffusion within the gamma phase up to the gamma /gamma ' interface. It is demonstrated that dissolution is affected by heating rate as well as the precipitate size. Below a threshold heating rate of sim 0.1 {^circ }C s^{-1}, the dissolution kinetics are marginally affected, however, is sensitive to microstructure. The role of precipitate size during dissolution is governed by diffusion flux in the gamma phase at the gamma /gamma ' interface, which is inversely proportional to size. It is argued that numerical simulations that predict constitutional liquation during rapid heating by altering the width of the computation domain to match the average precipitate size of the gamma ' population will yield inaccurate predictions. The influence of the heating rate on the nucleation undercooling, during subsequent cooling, has also been addressed. With increasing heating rates, the local gamma ' solvus temperature is shifted to progressively higher temperatures. Unless complete dissolution of gamma ' occurs prior to subsequent cooling, erroneous interpretations of nucleation undercooling can arise.

Magnetic Domain Structure of Galfenol at Elevated Temperatures

Galfenol (iron–gallium) has a great potential in MEMS applications owing to its high magnetostriction constant, low saturation field, and resilience to bending, compressive, and tensile loading. Here, we report on the expansion/shift of the topography and the expansion/shift of the magnetic domain structure of galfenol observed at high temperatures via atomic force microscopy (AFM) and magnetic force microscopy (MFM). The maze-like domain pattern and stripe-like domain pattern are observed in the perpendicular and parallel surfaces. The spike and reverse domains are observed in 3-D view via XEI imaging software. A MATLAB-based stereological method was used to obtain the domain width and domain wall energy density. An increase in domain width and decrease in domain wall energy density was identified when temperature increased from room temperature to 150 °C.

Strong memory effect in higher α-olefin homopolymers with crystalline side chains

The homopolymers of higher α-olefins with 12–20 carbon atoms were successfully synthesized using the dimethylpyridylamidohafnium/organoboron catalyst. With these model samples, the relationship between crystallization and chain topology were investigated employing the differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The DSC results show that for these homopolymers of higher α-olefins, the crystallization temperature is significantly elevated with increasing the length of side chains. The WAXD evidences demonstrate that cooling crystallization of these homopolymers at 10 °C/min can form the Type ІІ crystallites with zigzag arrangement of side chains. Interestingly, these higher α-olefin homopolymers exhibit the strong memory effect of crystallization, where the accelerated crystallization of poly(1-hexadecene) was observed after annealing at the elevated temperature up to 70 °C higher than melting range. Quantitatively, the temperature width of memory Domain II changes in a bell type with increasing side-chain length, where poly(1-hexadecene) shows the largest Domain II width of 74 °C. However, the strong memory effect beyond the melting range that is observed for the Type ІІ crystallites, is absent in Type І crystallites packed by the main chains, as demonstrated by the results of poly(1-tetradecene). Moreover, it was found that this memory effect of Type II crystallites is stable and independent on the annealing time.

Effect of Ordered Phases and Microstructures on the Iron Loss of 6.5 wt% Si Electrical Steel Quenched at Various Cooling Rates

Herein, the effect of the ordered phases and microstructure of 6.5 wt% Si electrical steel recrystallized and quenched at different cooling rates on its iron loss is investigated. The varied cooling rate barely influences the grain size and the precipitation of Cu but affects the magnetic domain significantly. A higher cooling rate is associated with greater residual stress and hence, leads to an increase in the width of the magnetic domain. In terms of the ordered phases, the quantity of B2 first decreases and then increases with a rising cooling rate while the quantity of D03 decreases. Meanwhile, the size of B2 antiphase domains reduces, while the D03 antiphase domains are either too fine to be observed or absent at higher cooling rates. The increased residual stress, the refinement of B2 antiphase domains, and the associated larger pinning effect on the migration of magnetic domain walls jointly lead to higher hysteresis loss. In addition, the increased width of the magnetic domain results in a larger anomalous loss. Both effects give rise to an overall increase in the iron loss P10/50.

Nanoscale magnetic bubbles in Nd2Fe14B at room temperature

The increasing demand for computer data storage with a higher recording density can be addressed by using smaller magnetic objects, such as bubble domains. Small bubbles predominantly require a strong saturation magnetization combined with a large magnetocrystalline anisotropy to resist self-demagnetization. These conditions are well satisfied for highly anisotropic materials. Here, we study the domain structure of thin ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$ lamellae. Magnetic bubbles with a minimum diameter of 74 nm were observed at room temperature, approaching even the range of magnetic skyrmions. The stripe domain width and the bubble size are both thickness dependent. Furthermore, a kind of bubble was observed below the spin-reorientation transition temperature that combine bubbles with opposite helicity. In this paper, we reveal ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$ to be a good candidate for a high-density magnetic bubble-based memory.