Domain Evolution Research Articles

Excellent energy storage performance in BSFCZ/AGO/BNTN double-heterojunction capacitors via the synergistic effect of interface and dead-layer engineering

Dielectric films with ultra-high energy storage density and efficiency are urgently needed due to the energy crisis. Here, we construct novel ferroelectric/dead-layer/superparaelectric (FE/DL/SPE) double-heterojunction capacitors, utilizing interface and dead-layer engineering to achieve outstanding energy storage performance. Bi0.9Sm0.1Fe0.9Co0.05Zn0.05O3 (BSFCZ) with large polarization, Ba0.985Na0.015Ti0.95Ni0.05O3 (BNTN) with low hysteresis and high breakdown strength (Eb), and artificial Al0.9Ga0.1O3 (AGO) with wide band-gap were chosen as the FE, SPE, and DL phases, respectively. Interface engineering enables the BSFCZ/AGO/BNTN films to maintain a high polarization of 55 μC cm−2, while the linear dielectric AGO and SPE BNTN substantially suppresses the remnant polarization. This can be clarified by the evolution of domains in the BSFCZ layer: nanodomains are scaled down to polar clusters, reducing polarization hysteresis while maintaining relatively high polarization. Simultaneously, two opposing intrinsic electric fields are formed to offset a portion of the external electric field, and the low dielectric constant AGO layer bears a significant part of the applied electric field due to electromagnetic boundary conditions. Consequently, the Eb is significantly increased from 4.4 MV cm−1 of BSFCZ/BNTN to 5.5 MV cm−1 of BSFCZ/AGO/BNTN, resulting in a giant recoverable energy density of 132 J cm−3 and a high efficiency of 84 % in BSFCZ/AGO/BNTN films. Moreover, the BSFCZ/AGO/BNTN films excel in temperature stability (RT∼200 °C), fatigue resistance (up to 107 cycles), and frequency stability (200 Hz to 20 kHz), alongside an exceptionally rapid discharge rate of 2.6 μs. This innovative approach suggests new possibilities for producing environmentally friendly, large-area, high-performance dielectric capacitors.

Probing intrinsic magnetic domain in bare CrI3 bulk with a magnetic force microscope

Two-dimensional magnetism in CrI3 links to its stacking structural order. In bulk CrI3, coexistence of monoclinic and rhombohedral phases has been observed across wide temperature range. Direct characterization of the magnetic textures on the exposed surface of bulk CrI3 has been challenging but meaningful. Here, we have employed a custom glovebox-assisted magnetic force microscope to observe the evolution of magnetic domains on the bare CrI3 surface under variable temperatures and magnetic fields for the first time. Below the Curie temperature, robust parallel stripe magnetic domains spontaneously emerge. The root mean square values of the localized weak pinning domain images at various temperatures indicate a critical transition behavior consistent with 3D Ising model with Tc ∼ 59 K. Images obtained by varying the magnetic field at low temperatures, showing magnetization saturation-reentry cycles, reveal larger hysteresis and stronger disorder compared to the VSM measurement, indicating local structural phase inhomogeneity. ​Two in-plane stripe magnetic domains oriented locally at an angle of 51-degrees compete under an out-of-plane magnetic field, presumably due to different sliding orientations induced by the magnetic field during the transition from a monoclinic to a rhombohedral phase. This study provides an experimental reference for future spin density wave manipulation in CrI3.

Neoproterozoic crustal evolution of Indo-Australo-Antarctic Suture domain and Gamburtsev Subglacial Mountains, East Antarctica: Insights from offshore sediments

Princess Elizabeth Land (PEL) preserves an intricate amalgamation of complexly intersecting orogenic belts of the Gondwanian age cross cut by the ramified East Antarctic Rift system. Indo-Australo-Antarctic Suture (IAAS) is an extensive orogenic zone connecting the Africo-Antarctic domain of Dronning Maud Land to the Australo-Antarctic domain of Wilkes Land region through the Indo-Antarctic domain of Princess Elizabeth Land, touching the northern boundary of the Gamburtsev Subglacial Mountains (GSMs). The GSMs and IAAS, located in the interior of PEL, are completely hidden within the ice sheet. The connection between the IAAS and concealed GSMs remains ambiguous due to insufficient geological evidence. Marine sediments from Prydz Bay offer clues to explore this segment of PEL. In this work, sediments from Ocean Drilling Program (ODP) sites: 740, 742, and 739, representing proximal to relatively distal sites, respectively, were subjected to geochemical and zircon isotopic analyses to understand the crustal evolution of PEL, IAAS, and GSM. The sediment geochemistry indicates that sediments from site 740, being proximal, are immature, less recycled, and more chemically weathered as compared to sites 742 and 739. Discriminant plots of major and trace elements provide active and passive continental margin signatures. Site 739 and 742 sediments display the rift setting signatures while sediments of site 740 depict signatures of collisional setting supporting the presence of an orogenic belt in the interior of PEL. Zircons from the proximal sites display age ranges from Paleoproterozoic to Pan-African. Zircons from the distal site predominantly show ages ∼650 Ma, hinting at the possibility of a Tonian-Cryogenian event in the hinterland of the PEL sector, possibly in the GSMs. Our results provide a better understanding of the Neoproterozoic crustal evolution of the IAAS domain of the PEL sector.

The Role of Interfacial Interactions and Oxygen Vacancies in Tuning Magnetic Anisotropy in LaCrO3/LaMnO3 Heterostructures

AbstractThe interplay of lattice, electronic, and spin degrees of freedom at epitaxial complex oxide interfaces provides a route to tune their magnetic ground states. Unraveling the competing contributions is critical for tuning their functional properties. The relationship between magnetic ordering and magnetic anisotropy and the lattice symmetry, oxygen content, and film thickness in compressively strained LaMnO3 (LMO)/LaCrO3 (LCO) superlattices is investigated. Mn–O–Cr antiferromagnetic superexchange interactions across the heterointerface result in a net ferrimagnetic magnetic structure. Bulk magnetometry measurements reveal isotropic in‐plane magnetism for as‐grown oxygen‐deficient thin samples due to equal fractions of orthorhombic a+a‐c‐, and a‐a+c‐ twin domains. As the superlattice thickness is increased, in‐plane magnetic anisotropy emerges as the fraction of the a+a‐c‐ domain increases. On annealing in oxygen, the suppression of oxygen vacancies results in a contraction of the lattice volume, and an orthorhombic to rhombohedral transition leads to isotropic magnetism independent of the film thickness. The complex interactions are investigated using high‐resolution synchrotron diffraction and X‐ray absorption spectroscopy. These results highlight the role of the evolution of structural domains with film thickness, interfacial spin interactions, and oxygen‐vacancy‐induced structural phase transitions in tuning the magnetic properties of complex oxide heterostructures.

Experimental Observation of the Fully Ferroelectric-Fully Ferroelastic Effect in Multiferroic Hybrid Perovskites.

Since the concept of "multiferroic" was first proposed in 1968, the coupling effect between different ferroic orders has attracted great interest in energy, information, and biomedical fields. However, the fully ferroelectric-fully ferroelastic effect has never been experimentally observed in hybrid perovskites, even though this effect was predicted to exist half a century ago. Realizing such cross-linking effects of polarization vectors and strain tensors has always been a huge challenge because of the complex difference in these two ferroic origins. Here, we report a multiferroic with full ferroelectricity and full ferroelasticity in two-dimensional (2D) hybrid perovskites based on ferroelectrochemistry. The dynamic molecular reorientations endow (cyclohexanemethylaminium)2PbCl4 with a desired symmetry change of 4̅2mFmm2 at a Curie temperature of 411.8 K. More strikingly, the switchable evolution of ferroelastic domains was directly observed under the control of either electric or mechanical fields, which is the first experimental observation of a fully ferroelectric-fully ferroelastic effect in hybrid perovskites. This work would provide new insights into understanding the intrinsic cross-linking mechanism between ferroelectricity and ferroelasticity toward the development of multichannel interactive microelectronic devices.

A micromagnetic-mechanically coupled phase-field model for fracture and fatigue of magnetostrictive alloys

Magnetostrictive alloys are usually brittle materials with micromagnetic structures. Their structural reliability and durability depend on the complex micromagnetic-mechanical coupling at smaller length scales encompassing the evolution of micromagnetic structures. Herein we propose a micromagnetic-mechanically coupled phase-field model for fracture and fatigue behavior of magnetostrictive alloys with evolution of the micromagnetic structure. The thermodynamically-consistent model is derived from microforce theory, laws of thermodynamics, and Coleman–Noll analysis. The evolution of crack phase-field and magnetization-vector order parameters that are fully coupled is governed by history field dependent Allen–Cahn and Landau–Lifshitz–Gilbert equations, respectively. The model is extended to fatigue by introducing a degradation prefactor for the fracture energy as a function of positive elastic energy. One-dimensional analyses are then presented to anatomize the crack driving forces in terms of fully coupled micromagnetic-mechanical and pure mechanical driving force. We demonstrate the model capabilities by finite-element numerical studies on the micromagnetic domain evolution during the crack propagation and the influence of external magnetic field for type-I, type-II, and three-point bending fracture, as well as for the fracture of a single-edge notched specimen with an elliptical inclusion. The simulation result shows that depending on how micromagnetic domains are switched under micromagnetic-mechanical coupling, the magnetic field can enhance or decrease the critical load. In the presence of inclusion with larger fracture toughness, a crack is found to nucleate in the tri-junction of multi-domain micromagnetic structure owing to the high elastic strain around the tri-junction point. It is further found that a suitable magnetic field promoting magnetization-vector rotation around the crack tip could remarkably improve the fracturing load and fatigue life. The results demonstrate the model promising for the study of micromagnetic-mechanically coupled fracture and fatigue in magnetostrictive alloys.

Temperature and medium structurization effect on spontaneous evolution of domains and bubbles in magnetic nanostructures

Spontaneous evolutions of domains in magnetic nanowires and of magnetic bubbles in open ferromagnetic nanolayers are investigated using micromagnetic simulations. We compare temperature dependent dynamics of domain wall (DW) systems in Permalloy (Py) nanowires and systems of chiral DWs in ultra-thin nanowires with perpendicular magnetic anisotropy (PMA) and Dzyaloshinskii-Moriya interaction (DMI). In Py nanowires DWs collide and, in majority of cases, the collision leads to the DW annihilation in disagreement with the expectation of topological protection of sums of all the magnetic charges attached to the nanowire edges which are carried by DWs. For our purpose of discussing the DW collision in the presence of thermal excitations, we revisit the problem of field-driven collisions of DWs in Py nanowires at zero temperature. We claim that thermal fluctuations can counteract the collision-induced annihilation of DWs, thought further improvement of stabilization of domain structures is achievable via structurization of the magnetic nanowires (dividing them into grains). In PMA-DMI nanowires, thermally-excited chiral DWs can be randomly approaching or moving away while not being annihilated. A problem related to the motion of chiral DWs is the spontaneous motion of magnetic bubbles in open PMA-DMI planes. The magnetic bubbles expand or shrink to vanishing dependent on strength of the DMI interaction. Such a motion appears to be be strongly influenced by temperature and by structural discontinuities of the magnetic layer.

Manipulation of Moiré Superlattice in Twisted Monolayer-multilayer Graphene by Moving Nanobubbles.

In the heterostructure of two-dimensional (2D) materials, many novel physics phenomena are strongly dependent on the Moiré superlattice. How to achieve the continuous manipulation of the Moiré superlattice in the same sample is very important to study the evolution of various physical properties. Here, in minimally twisted monolayer-multilayer graphene, we found that bubble-induced strain has a huge impact on the Moiré superlattice. By employing the AFM tip to dynamically and continuously move the nanobubble, we realized the modulation of the Moiré superlattice, like the evolution of regular triangular domains into long strip domain structures with single or double domain walls. We also achieved controllable modulation of the Moiré superlattice by moving multiple nanobubbles and establishing the coupling of nanobubbles. Our work presents a flexible method for continuous and controllable manipulation of Moiré superlattices, which will be widely used to study novel physical properties in 2D heterostructures.

Aquathermal effect of anomalous pressure generation in consolidating minefill

Recycling cement-amended tailings into subsurface cavities has delivered competitive socioeconomic revenue for underground mining. However, recent instances of anomalous thermal pressure in consolidating backfill have raised growing concerns over the current design philosophy. This study demonstrates that the excellent hydraulic sealing and considerable chemical energy inherent in cemented backfill can spontaneously generate substantial thermal pressurisation through constrained pore fluid expansion. An analytical solution is hence developed for characterising the non-isothermal behaviour of hydrating backfill based on classical thermo-poroelasticity. The influence of the preparation condition and mix design on the pressure evolution in the time domain and during spontaneous heat generation is then thoroughly examined, successfully pinpointing the causal mechanism responsible for typical thermal pressure anomalies. It is demonstrated that the anomalous pressure is attributable to both the conservative use of binder, which increases the intrinsic heat load, and the elevated initial temperature, which promotes water volume expansion. The fundamental influence of temperature-sensitive water expansivity on the path dependence of thermal pressurisation is also elucidated. This study thus contributes to a comprehensive understanding of the thermally correlated pressure anomalies that frequently occur in field operations. These critical findings would also hold practical implications for designing successful backfill solutions in challenging mine environments.

A Bibliometric Analysis of the Role and Research Trending of Bronchoalveolar Lavage in the Diagnosis and Treatment of Ventilator-Associated Pneumonia.

Ventilator-associated pneumonia (VAP) is one of the most common complications in intensive care units (ICUs) and negatively affects patient outcomes. Despite its widespread use as a diagnostic and therapeutic measure, the application and effectiveness of bronchoalveolar lavage (BAL) in the management of VAP require further exploration. This study aimed to evaluate the research dynamics, major trends, and scientific networks of BAL in the diagnosis and treatment of VAP using bibliometric analysis. Literature from the Web of Science database on BAL for the diagnosis and treatment of VAP from 1990 to 2024 was screened and analyzed. Keyword co-occurrence, trend analysis, and citation burst analyses were conducted using CiteSpace to identify research hotspots, core authors, institutions, and countries, as well as the evolution of research domains. The bibliometric analysis included 968 publications. Trend analysis indicated growing interest in BAL techniques, particularly in the categories of RESPIRATORY SYSTEM (burst score: 27.82) and MEDICINE, RESEARCH, and EXPERIMENTAL (burst score: 7.41). The co-citation analysis highlighted influential authors in the field, such as Torres(burst score: 9.35), Croce (burst score: 5.86), and Meduri(burst score: 5.71). Keyword analysis results revealed core clusters in the treatment of VAP with BAL, including "nonbronchoscopic lavage" (silhouette value: 0.703), "ICU-acquired infection" (silhouette value: 0.7), and "ventilator-associated tracheobronchitis" (silhouette value: 0.637). Additionally, geographic analysis showed that North America and Europe dominated the research in this field. Recently, research trends regarding protected specimen brushes and quantitative culture techniques have emerged. This study found broad applications of BAL in VAP management, especially in improving diagnostic accuracy and treatment outcomes. Optimized strategies such as improvement of lavage techniques and multidisciplinary collaboration may emerge as potential research hotspots in the future.

Influence of Structural Domain Evolution in Carbon Materials on the Selective Separation of Alkenes from Alkanes

Influence of Structural Domain Evolution in Carbon Materials on the Selective Separation of Alkenes from Alkanes

DANet: A spatio-temporal dynamics and Detail Aware Network for video prediction

Video prediction aims to predict the upcoming future frames by modeling the complex spatiotemporal dynamics from given videos. However, most existing video prediction methods still perform sub-optimal in generating high-visual-quality future frames. The reasons behind that are: 1) these methods struggle to reason accurate future motion due to extracting insufficient spatiotemporal correlations from the given frames. 2) The state transition units in the previous works are complex, which inevitably results in the loss of spatial details. When the videos contain variable motion patterns (e.g. rapid movement of objects) and complex spatial information (e.g. texture details), blurring artifacts and local absence of objects may occur in the predicted frames. In this work, to predict more accurate future motion and preserve more details information, we propose an end-to-end trainable dual-branch video prediction framework, spatiotemporal Dynamics and Detail Aware Network (DANet). Specifically, to predict future motion, we propose a SpatioTemporal Memory (ST-Memory) to learn motion evolution in the temporal domain from the given frames by transmitting the deep features along a zigzag direction. To obtain adequate spatiotemporal correlations among frames, the MotionCell is constructed in the ST-Memory to facilitate the expansion of the receptive field. The spatiotemporal attention is utilized in the ST-Memory to focus on the global variation of given frames. Additionally, to preserve useful spatial details, we design the Spatial Details Memory (SD-Memory) to capture the global and local dependencies of the given frames at the pixel level. Extensive experiments conducted on three public datasets for both synthetic and natural demonstrate that the DANet has excellent performance for video prediction compared with state-of-the-art methods. In brief, DANet outperforms the state-of-the-art methods in terms of MSE by 3.1, 1.0×10−2 and 14.3 × 10 on three public benchmark datasets, respectively.

Effect of magnetic field on macroscopic hysteresis and microscopic magnetic domains for different ferromagnetic materials

The macroscopic hysteresis of ferromagnetic materials is influenced by their microscopic magnetic domains, establishing a correspondence between the two that enables a fundamental understanding of the magnetization process of ferromagnetic materials. Based on this, this study employs the phase field method to investigate the macroscopic hysteresis and microscopic magnetic domain evolution of soft, hard, and rectangular ferromagnetic materials. The hysteresis loops of the three materials present narrow, wide and rectangular characteristics respectively, which are quantitatively consistent with the experimental data. Subsequently, the influence of the magnetic field on the macroscopic hysteresis is analyzed. The results show that the hysteresis loop area increases when the magnetic field amplitude increases. Furthermore, the proportion of each type of energy under different magnetic fields is discussed, the dominant energy terms are generally consistent for the same category of ferromagnetic materials. Additionally, the corresponding magnetic domain evolution under different magnetic field is displayed, with soft magnetic materials exhibiting no vortex structures, hard ferromagnetic materials presenting a 45° vortex structure, and rectangular magnetic material showcasing a 90° vortex structure. Finally, the asymmetric characteristics of the major hysteresis loop and minor hysteresis loops are discussed. The change of the magnetic field path leads to the corresponding change of the major and minor hysteresis loops. At the same magnetic field, distinctions in magnetic domain configurations between the major and minor hysteresis loops are evident.

Promotion of Probabilistic Bit Generation in Mott Devices by Embedded Metal Nanoparticles.

Considerable attention has been drawn to the use of volatile two-terminal devices relying on the Mott transition for the stochastic generation of probabilistic bits (p-bits) in emerging probabilistic computing. To improve randomness and endurance of bit streams provided by these devices, delicate control of the transient evolution of switchable domains is required to enhance stochastic p-bit generation. Herein, it is demonstrated that the randomness of p-bit streams generated via the consecutive pulse inputs of pump-probe protocols can be increased by the deliberate incorporation of metal nanoparticles (NPs), which influence the transient dynamics of the nanoscale metallic phase in VO2 Mott switches. Among the vertically stacked Pt-NP-containing VO2 threshold switches, those with higher Pt NP density show a considerably wider range of p-bit operation (e.g., up to ≈300% increase in ΔVprobe upon going from (Pt NP/VO2)0 to (Pt NP/VO2)11) and can therefore be operated under the conditions of high speed (400 kbit s-1), low power consumption (14 nJ per bit), and high stability (>105200 bits) for p-bit generation. Thus, the study presents a novel strategy that exploits nanoscale phase control to maximize the generation of nondeterministic information sources for energy-efficient probabilistic computing hardware.

A phase-field model for study of ferroelastic deformation behavior in yttria stabilized zirconia

A modified phase-field model coupled with linear elasticity is formulated to study the effect of ferroelastic domain switching on the deformation behavior of tetragonal-prime yttria-stabilized zirconia. Simulations are performed under uniaxial tension and compression using realistic domain microstructures. This work provides new insights into the mechanism of ferroelastic deformation by studying the evolution of domains under different loading directions and strain rates. The model predicts realistic stress-strain curves consisting of stress-plateaus with accurate domain switching behavior without setting a switching criterion based on a critical stress for nucleation of new domains. The results reveal that the origin of coercive stress lies in the balance between the energy absorbed by the domain switching process and the externally applied energy. Loading in different directions but parallel to the spontaneous strain results in different levels of coercive stress as domain switching absorbs different amounts of energy. For the same reason when the strain-rate increases, the coercive stress also increases. This work establishes the relation between the coercive stress and microstructural changes during ferroelastic domain switching.

Untangling the Evolution of the Receptor-Binding Motif of SARS-CoV-2

The spike protein determines the host-range specificity of coronaviruses. In particular, the Receptor-Binding Motif in the spike protein from SARS-CoV-2 contains the amino acids involved in molecular recognition of the host Angiotensin Converting Enzyme 2. Therefore, to understand how SARS-CoV-2 acquired its capacity to infect humans it is necessary to reconstruct the evolution of this important motif. Early during the pandemic, it was proposed that the SARS-CoV-2 Receptor-Binding Domain was acquired via recombination with a pangolin infecting coronavirus. This proposal was challenged by an alternative explanation that suggested that the Receptor-Binding Domain from SARS-CoV-2 did not originated via recombination with a coronavirus from a pangolin. Instead, this alternative hypothesis proposed that the Receptor-Binding Motif from the bat coronavirus RaTG13, was acquired via recombination with an unidentified coronavirus. And as a consequence of this event, the Receptor-Binding Domain from the pangolin coronavirus appeared as phylogenetically closer to SARS-CoV-2. Recently, the genomes from coronaviruses from Cambodia (bat_RShST182/200) and Laos (BANAL-20-52/103/247) which are closely related to SARS-CoV-2 were reported. However, no detailed analysis of the evolution of the Receptor-Binding Motif from these coronaviruses was reported. Here we revisit the evolution of the Receptor-Binding Domain and Motif in the light of the novel coronavirus genome sequences. Specifically, we wanted to test whether the above coronaviruses from Cambodia and Laos were the source of the Receptor-Binding Domain from RaTG13. We found that the Receptor-Binding Motif from these coronaviruses is phylogenetically closer to SARS-CoV-2 than to RaTG13. Therefore, the source of the Receptor-Binding Domain from RaTG13 is still unidentified. In accordance with previous studies, our results are consistent with the hypothesis that the Receptor-Binding Motif from SARS-CoV-2 evolved by vertical inheritance from a bat-infecting population of coronaviruses.

Magnetic domain structures in ultrathin Bi2Te3/CrTe2 heterostructures

Abstract Chromium tellurium compounds are important two-dimensional van der Waals ferromagnetic materials with high Curie temperature and chemical stability in air, which is promising for applications in spintronic devices. Here, high-quality spin-orbital-torque (SOT) device, Bi2Te3/CrTe2 heterostructure was epitaxially grown on Al2O3 (0001) substrates. Anomalous Hall measurements indicate the existence of strong ferromagnetism in this device with the CrTe2 thickness down to 10 nm. In order to investigate its micromagnetic structure, cryogenic magnetic force microscope (MFM) was utilized to measure the magnetic domain evolutions at various temperatures and magnetic fields. The virgin domain state of the device shows a worm-like magnetic domain structure with the size around 0.6 ~ 0.8 µm. Larger irregular-shape magnetic domains (＞1µm) can be induced and pinned, after the field is increased to coercive field and ramped back to low fields. The temperature-dependent MFM signals exhibit a nice mean-field-like ferromagnetic transition with Curie temperature around 201.5 K, indicating a robust ferromagnetic ordering. Such device can be potentially implemented in future magnetic memory technology.

Ceramic-Based Dielectric Materials for Energy Storage Capacitor Applications.

Materials offering high energy density are currently desired to meet the increasing demand for energy storage applications, such as pulsed power devices, electric vehicles, high-frequency inverters, and so on. Particularly, ceramic-based dielectric materials have received significant attention for energy storage capacitor applications due to their outstanding properties of high power density, fast charge-discharge capabilities, and excellent temperature stability relative to batteries, electrochemical capacitors, and dielectric polymers. In this paper, we present fundamental concepts for energy storage in dielectrics, key parameters, and influence factors to enhance the energy storage performance, and we also summarize the recent progress of dielectrics, such as bulk ceramics (linear dielectrics, ferroelectrics, relaxor ferroelectrics, and anti-ferroelectrics), ceramic films, and multilayer ceramic capacitors. In addition, various strategies, such as chemical modification, grain refinement/microstructure, defect engineering, phase, local structure, domain evolution, layer thickness, stability, and electrical homogeneity, are focused on the structure-property relationship on the multiscale, which has been thoroughly addressed. Moreover, this review addresses the challenges and opportunities for future dielectric materials in energy storage capacitor applications. Overall, this review provides readers with a deeper understanding of the chemical composition, physical properties, and energy storage performance in this field of energy storage ceramic materials.

Elevated temperature magnetic microstructures and demagnetization mechanism for grain boundary diffused dual-main-phase (Nd, Ce)-Fe-B magnets

The combination of dual-main-phase (DMP) (Nd, Ce)-Fe-B magnets and grain boundary diffusion process (GBDP) is currently a research topic for obtaining high-cost performance materials in rare earth permanent magnet fields. The novel structural features of GBDP (Nd, Ce)-Fe-B magnets give a version of different domain reversal processes from those of non-diffused magnets. In this work, the in-situ magnetic domain evolution of the DMP magnets was observed at elevated temperatures, and the temperature demagnetization and coercivity mechanism of the GBDP dual-main-phase (Nd, Ce)-Fe-B magnets are discussed. The results show that the shell composition of different types of grains in DMP magnets is similar, while the magnetic microstructure results indicate the Ce-rich grains tend to demagnetize first. Dy-rich shell with a high anisotropic field caused by GBDP leads to an increase in the nucleation field, which enhances the coercivity. It is found that much more grains exhibit single domain characteristics in the remanent state for GBDP dual-main-phase (Nd, Ce)-Fe-B magnets. In addition, the grains that undergo demagnetization first are Ce-rich or Nd-rich grains, which is different from that of non-diffused magnets. These results were not found in previous studies but can be intuitively characterized from the perspective of magnetic domains in this work, providing a new perspective and understanding of the performance improvement of magnetic materials.

Molecular beam epitaxy and characterization of ferroelectric quaternary alloy Sc0.2Al0.45Ga0.35N

In this study, we demonstrate ferroelectricity in high-quality monocrystalline quaternary alloy ScAlGaN. Sc0.2Al0.45Ga0.35N films are grown by plasma-assisted molecular beam epitaxy and exhibit a surface roughness of 0.5 nm, limited by the roughness of the underlying molybdenum template. Polarization-electric field and positive-up-negative-down measurements reveal unambiguous ferroelectric switching with a coercive field of ∼5.5 MV cm−1 at 10 kHz and high remanent polarization of ∼150 μC cm−2. Time-dependent measurements suggest that the polarization reversal behavior adheres to the Kolmogorov–Avrami–Ishibashi model and follows a scheme of domain nucleation and growth. Detailed piezoresponse force microscopy studies further elucidate the evolution of polarity reversal domains in wurtzite nitride ferroelectrics and support the notion that the growth of inversion domains occurs via an in-plane motion of the domain walls. The realization of functional ferroelectric quaternary alloys in the wurtzite nitride family extends beyond being a technical demonstration. The additional degree of bandgap, band alignment, lattice parameter, and piezoelectric constant tunability achievable through quaternary alloys unveils a vast dimension through which wurtzite nitride ferroelectrics can be optimally engineered for a broad variety of high-performance electronic, optoelectronic, and acoustic devices and systems.