Fe Domains Research Articles

(Invited) Engineering Nanocomposite Substrates for Metal Deposition

Reversible metal plating is at the heart of aqueous based energy storage. Since virtually all metal anodes, e.g., Fe, and Zn, operate outside the stability window of water, it is thus essential to minimize their surface area by controlling the nucleation and growth during deposition and the pit formation during stripping.While epitaxial growth has shown promise as exemplified by the horizontal zinc deposition on graphene, an approximate heteroepitaxy, we will focus our effort in developing a nanocomposite substrate that promotes uniform nucleation sites and fast surface transport. The strategy is potentially highly scalable to address the need for large scale storage. Recently, we have shown that a nanocomposite substrate can induce single crystalline Li growth. By reacting FeF3 with Li, a nanocomposite of Fe and LiF is formed which features Fe nanoparticles of < 2 nm in size uniformly distributed in a matrix of LiF. Despite the global lithiophobility of the substrate, nano Fe domains provide energetically uniform nucleation sites for Li deposition while LiF enables rapid surface transport. Corporative merging of neighboring seeds lead to the formation of single crystalline Li. Unlike single crystal substrates, the nanocomposite features uniformly distributed, energetically equivalent sites for nucleation.We have adopted a similar strategy for Fe and Zn deposition. Preliminary results show that significantly improved macroscopic uniformity is achieved with the nanocomposite substrate. We will discuss materials requirements for operation in an aqueous environment and the general applicability of the approach for other materials.

Ultralow‐Power Compact Artificial Synapse Based on a Ferroelectric Fin Field‐Effect Transistor for Spatiotemporal Information Processing

Artificial synapses are key elements in building bioinspired, neuromorphic computing systems. Ferroelectric field‐effect transistors (FeFETs) with excellent controllability and complementary metal oxide semiconductor (CMOS) compatibility are favorable to achieving synaptic functions with low power consumption and high scalability. However, because of the only nonvolatile ferroelectric (Fe) characteristics in the FeFET, it is difficult to develop bioplausible short‐term synaptic elements for spatiotemporal information processing. By judiciously combining defects (DE) and Fe domains in gate stacks, a compact artificial synapse featuring spatiotemporal information processing on a single Fe–DE fin FET (FinFET) is proposed. The devices are designed to work in a separate DE mode to induce short‐term plasticity by spontaneous charge detrapping, and a hybrid Fe–DE mode to trigger long‐term plasticity through the coupling of defects and Fe domains. The capability of the compact synapse is demonstrated by differentiating 16 temporal inputs. Moreover, the highly controllable static electricity of advanced FinFETs leads to an ultralow power of 2 fJ spike−1. An all Fe–DE FinFET reservoir computing (RC) system is then constructed that achieves a recognition accuracy of 97.53% in digit classification. This work enables constructing RC systems with fully advanced CMOS‐compatible devices featuring highly energy‐efficient and low‐hardware systems.

Hybridize magnesium-iron layered double hydroxide with biopolymers to develop multiple pathways for phosphate sorption and release: A potential slow release phosphorus fertilizer

The intensive use of chemical fertilizers presents a dilemma for sustaining food production or causing soil degradation and posing agricultural contamination. The reduction of phosphorus (P) fertilizer usage is particularly crucial because it is a limited resource. This situation calls for the development of efficient P fertilizers to address the impending P deficiency. Mg-Fe layered double hydroxides (LDH) with 0.5 and 2.5 M metal precursors were hybridized with chitosan (CTS) and carboxymethyl cellulose (CMC) to design alternatives of slow release P fertilizers. While phosphate (PO4) sorption capacities were in the order of Mg-Fe LDH > 2.5LDH-CTS/CMC > 0.5LDH-CTS/CMC, PO4 release from 0.5LDH-CTS exhibited a rate constant ∼2.6–7.6 times lower than that of other samples, which had not reached equilibration even after 2688 h. Fe-EXAFS data implied the greatest degree of isomorphic substitution into LDH interlayer of 0.5LDH-CTS. In addition to intercalated PO4, P-XANES data also suggested the organic-P and Fe(III)-P on 0.5LDH-CTS, causing versatile retention processes. After 2688 h of PO4 release, LDH structure gradually weathered and transformed primarily into a structure dominated by ferric (oxyhydrox)oxides. On 0.5LDH-CTS, however, 14.3% of Fe inventory was contributed by Fe(II) species. The Fe(II) domains in conjunction with the likely remaining Mg-Fe LDH structure and amorphous Mg(OH)2 provided bonding sites for PO4, serving as the key factor for the continuous PO4 release beyond 2688 h. Such extended duration of PO4 release warrants the use of LDHs hybridized with biopolymers as promising substitutes for slow release P fertilizers.

Synergism of Fe and Al salts for the coagulation of dissolved organic matter: Structural developments of Fe/Al-organic matter associations

Dissolved organic matter (DOM) is distributed ubiquitously in water bodies. Ferric ions can flocculate DOM to form stable coprecipitates; however, Al(III) may alter the structures and stability of Fe-DOM coprecipitates. This study aimed to examine the coprecipitation of Fe, Al, and DOM as well as structural developments of Fe-DOM coprecipitates in relation to changes in Fe/Al ratios and pHs. The results showed that the derived Fe/Al/DOM-coprecipitates could be classified into three categories: (1) at pH 3.0 and 4.5, the corner-sharing FeO6 octahedra associated with Fe–C bonds with Fe/(Fe + Al) ratios ≥0.5; (2) the Fe–C bonds along with single Fe octahedra having Fe/(Fe + Al) ratios of 0.25; (3) at pH 6.0, the ferrihydrite-like Fe domains associated with Fe–C bonds with Fe/(Fe + Al) ratios ≥0.5. At pH 3.0, the Fe and C stability of the coprecipitates increased with increasing Al proportions; nonetheless, pure Al-DOM coprecipitates were unstable even if they exhibited the maximum ability for DOM removal. The associations of Al-DOM complexes and/or DOM-adsorbed Al domains with external surfaces of Fe domain or Fe-DOM coprecipitates may stabilize DOM, leading to lower C solubilization at pH 4.5. Although the preferential formation of Fe/Al hydroxides decreased Fe/Al solubilization at pH 6.0, adsorption instead of coprecipitation of DOM with Fe/Al hydroxides may decrease C stabilization in the coprecipitates. Aluminum cations inhibit DOM releases from Fe/Al/DOM-coprecipitates, promoting the treatment and reuse efficiencies of wastewater and resolving water shortages. This study demonstrates that Al and solution pH greatly affect the structural changes of Fe-DOM coprecipitates and indirectly control the dynamics of Fe, Al, and C concentrations in water.

Leveraging Ferroelectric Stochasticity and In-Memory Computing for DNN IP Obfuscation

With the emergence of the Internet of Things (IoT), deep neural networks (DNNs) are widely used in different domains, such as computer vision, healthcare, social media, and defense. The hardware-level architecture of a DNN can be built using an in-memory computing-based design, which is loaded with the weights of a well-trained DNN model. However, such hardware-based DNN systems are vulnerable to model stealing attacks where an attacker reverse-engineers (REs) and extracts the weights of the DNN model. In this work, we propose an energy-efficient defense technique that combines a ferroelectric field effect transistor (FeFET)-based reconfigurable physically unclonable function (PUF) with an in-memory FeFET XNOR to thwart model stealing attacks. We leverage the inherent stochasticity in the FE domains to build a PUF that helps to corrupt the neural network’s (NN) weights when an adversarial attack is detected. We showcase the efficacy of the proposed defense scheme by performing experiments on graph-NNs (GNNs), a particular type of DNN. The proposed defense scheme is a first of its kind that evaluates the security of GNNs. We investigate the effect of corrupting the weights on different layers of the GNN on the accuracy degradation of the graph classification application for two specific error models of corrupting the FeFET-based PUFs and five different bioinformatics datasets. We demonstrate that our approach successfully degrades the inference accuracy of the graph classification by corrupting any layer of the GNN after a small rewrite pulse.

On the thickness dependence of the polarization switching kinetics in HfO2-based ferroelectric

HfO2-based ferroelectric (FE–HfO2) is a promising material for low-power and high-capacity memory technology. Since thinner ferroelectric films are required for low voltage operation, the impact of film thickness on the switching kinetics of FE–HfO2 needs to be studied in detail. In this paper, metal/ferroelectric/metal capacitors are fabricated with several thicknesses of HfZrO2 (HZO) films and characterized to study the switching kinetics based on the nucleation limited switching (NLS) model. Thinner HZO capacitors show slower polarization switching and asymmetry in program and erase operation, although low-frequency polarization charge density is nearly the same for all thicknesses. Slow switching is due to the large variability of the activation field of FE domains and grain boundaries among small FE grains. The asymmetry is caused by the asymmetric interface property at the top and bottom interfaces. High-resolution TEM and electron diffraction mapping methods provide physical evidence for the above discussions.

Coupled Current Jumps and Domain Wall Creeps in a Defect‐Engineered Ferroelectric Resistive Memory

AbstractFerroelectric (FE) resistive switching has attracted considerable interest as a promising candidate for applications in non‐volatile memory technology. In this work, via judiciously controlling the defect states of oxygen vacancy through Sm‐doping, the authors obtain multiple current jumps/discrete resistance states in the resistive switching memories based on a model FE BiFeO3 (BFO). These hitherto unreported current jumps are attributed to the space‐charge‐limited current correlated with electron trapping by oxygen vacancies in the BFO film. Concurrently, oxygen vacancies serve as the pinning centers for the FE domains, leading to the domain wall creep behavior. These results illustrate the strong interplay between the defect, resistive switching, and domain wall creep behavior in FE diodes, providing a new insight into the mechanism of FE resistive switching. Overall, the large on/off ratio of ≈5 × 105, multiple resistance states, and fast switching speed of ≈30 ns, promise their potential applications in multi‐level data storage memories.

Tuning the stress state in Nb-thin films by lateral size confinement

For 5 nm thin Nb films adhered to a rigid substrate, hydrogen absorption leads to ultrahigh mechanical stress of about -8 GPa. This is related to a purely elastic behaviour. The high mechanical stress destabilizes phases and even suppresses conventional two-phase regions known for the Nb-H bulk system. These unique thin film properties can be preserved to thicker films, by lateral confinement. Nb-Fe films provide a laterally confined columnar domain structure of well-separated α-Nb(Fe) and μ-FeNb phases. While the α-Nb(Fe) absorbs hydrogen at low chemical potentials, the μ-FeNb phase does not, separating the two phases into a hydrogen active and a hydrogen passive one. The behaviour of 75 nm Nb-Fe films was studied by in situ mechanical stress measurements, in situ x-ray diffraction and transmission electron microscopy. With increasing Fe-content, Nb-Fe films show a strong increase in the yield stress upon hydrogen absorption. This allows for an extended elastic range and high maximum stress values of -4.6 GPa, for 75 nm Nb-Fe films. X-ray diffraction pattern collected upon hydrogen loading of Nb-Fe films show peak shifts and intermediate peak broadening. This indicates the presence of a two-phase region and preservation of the lattice coherency between the α-Nb(Fe)-H phase and the hydride phase. Peak shifts indicate a reduced vertical expansion of the hydrogen absorbing α-Nb(Fe) lattice. This is attributed to the presence of the µ-FeNb phase. FEM simulations on Nb-Fe-H films confirm reduced overall expansions and lateral stresses, when compared to pure Nb-H films. High vertical stresses arise upon H-loading due to the link between the two Nb-Fe phases. These stresses are tensile for µ-FeNb and compressive for the α-Nb(Fe) domains and also reach values of several GPa. Conservation of the exceptional thin film properties to thicker films by lateral confinement is suggested to be a powerful strategy for many different applications like sensor technologies or energy storage.

Carbon nanotube-supported bimetallic Cu-Fe catalysts for syngas conversion to higher alcohols

Catalytic transformation of syngas into higher alcohols is a challenging theme in C1 chemistry. The formation of higher alcohols require the synergy between active sites with abilities for CO dissociative and non-dissociative adsorption. This work reports Cu-Fe bimetallic catalysts loaded on carbon nanotubes (CNTs) for the conversion of syngas to higher alcohols. The structure-performance relationship for the catalysts prepared by different methods including co-impregnation and immobilization of pre-fabricated bimetallic nanoparticles have been investigated to gain insights into the effect of proximity of active sites on the formation of higher alcohols. We found that the Cu-Fe/CNT-co-red-imm catalyst, which was prepared by immobilization of colloidal bimetallic nanoparticles pre-fabricated with a co-reduction method, showed the closest proximity of Cu and Fe domains. This catalyst demonstrates the highest selectivity of higher alcohols. Our DFT calculation suggests that the coupling of surface CHO and CHx intermediates to form CH3CHO is a rate-limiting step. The DFT calculation also shows that the closer proximity between Fe2C (Fe) and Cu species leads to a lower energy barrier for the formation of CH3CH2OH from syngas.

Difference in Degrees of Satisfaction with Orthognathic Surgery and Orthodontic Treatment between Skeletal Class III and Cleft Patients.

The aim of this study was to compare the degrees of satisfaction with orthognathic surgery and orthodontic treatment between skeletal Class III and cleft patients. The samples consisted of Class III group (N = 25) and Cleft group (N = 16). The Modified Orthognathic Quality of Life Questionnaires, which had 5 domains (oral function [OF], awareness of dentofacial deformity [ADD], social relationship [SR], facial esthetics [FE], and nose/lip esthetics [NLE]), were evaluated with 5 rates (0 [very satisfactory] to 4 [very unsatisfactory]) at initial visit (T1), just before surgery (T2), 3 to 6 months after surgery (T3), and at debonding or 1 year after surgery (T4). The scores at each stage, amount of change between stages, and effect size (ES) in the 5 domains were investigated. Compared to Class III group, Cleft group exhibited lower satisfaction scores of NLE domain during all stages (all P < 0.001) and of SR domain and total domains at T4 stage (P < 0.05, P < 0.01). Cleft group showed significant improvement of satisfaction scores in FE domain during T1-T2 (P < 0.01), in SR, FE, NLE, and total domains during T2-T3 (all P < 0.01), in OF, SR, and total domains during T3-T4 (P < 0.05, P < 0.01, P < 0.01), and in all domains during T1-T4 (ADD, P < 0.05; OF, SR, and NLE, P < 0.01; FE and total, P < 0.001). Cleft group exhibited large improvement of ES only at SR and FE domains during T2-T3 (-0.81 and -1.09, respectively). Owing to lower satisfaction of NLE domain at all stages in cleft patients, clinicians should recommend adjunctive cosmetic surgery for nose and lip after completion of treatment.

Removal and simultaneous reduction of Cr(VI) by organo-Fe(III) composites produced during coprecipitation and coagulation processes.

Composites formed during the coprecipitation and/or coagulation of ubiquitous dissolved organic matter (DOM) and Fe in natural and waste water systems might be potential scavengers for Cr(VI) in terms of sorption and reduction. Our objective here was to determine sorption and simultaneous reduction of Cr(VI) on organo-Fe(III) composites (OFC) in relation coprecipitated pH and C/(C + Fe) ratios. Results showed the greatest Cr sorption of 51.8 mg g-1 on the OFC sample that was precipitated at pH 3 and contained the C/(C + Fe) molar ratio of 0.71. Wherein the Cr(VI) removal subsequent to the coprecipitation was dominated by the sorption on Fe hydroxides. Although amounts of total sorbed Cr decreased with increasing C/(C + Fe) molar ratio, the reverse trend on Cr(VI) reducibility compensated the Cr(VI) removal capability of OFC samples. With C/(C + Fe) molar ratios ≥ 0.89, the increasing amounts of coprecipitated organic matter that homogeneously distributed with Fe domains on OFC surfaces could trigger a significantly pronounced Cr reduction. Collectively, our results suggested an alternative method for Cr(VI) remediation by manipulating C/Fe ratios in suspensions. After the sorption of most Cr(VI) on Fe hydroxides, increasing C/Fe ratio in systems could further improve the Cr(VI) removal efficiency by the reduction of remaining Cr(VI) to Cr(III).

Effect of ferro-elastic twin domains of LaAlO3 substrate on the magnetic anisotropy and the magnetization reversal process of cobalt thin film

Abstract Present work reports the effects of ferroelastic domains (FE) on the magnetic properties of top magnetic layer. Cobalt film of 15 nm is deposited using electron beam evaporation technique on single crystalline LaAlO 3 (0 0 1) (LAO) substrate which consists FE structural twin domains. LAO substrate is in-situ heated above its FE transition temperature and cooled to room temperature before depositing cobalt film of 15 nm. Textured growth of cobalt film is observed in-situ from reflection high energy electron diffraction (RHEED) patterns. The presence of FE structural twins in LAO substrate is confirmed from the X-ray reciprocal space mapping measurements. From the optical polarization microscopy, it is observed that the different regions consist different modulations viz., lamellar like and square-like structures in LAO substrate. The magnetic anisotropy and magnetization reversal is studied ex-situ using magneto-optical Kerr effect (MOKE) microscopy with different spatial resolutions. The analysis of azimuthal variation of coercivity ( H C ) shows the superposition of two-, four- and six- fold anisotropy contribution at different regions of the sample. Twofold anisotropy and weak sixfold anisotropy may due to magneto-crystalline anisotropy, whereas the fourfold anisotropy might be coming because of square-like modulations of the substrate. Moreover, MOKE microscopy reveals the domain wall pinning along the twin boundaries (FE) due to which magnetization reversal is proceed by three distinct mechanisms when field is applied away from easy axis of magnetization and lamellar pattern. As a consequence of this, magnetization reversal proceeds by ‘labyrinth switching’ and abrupt magnetic domain wall switching within individual FE domains.

Phosphate Removal in Relation to Structural Development of Humic Acid-Iron Coprecipitates

Precipitation of Fe-hydroxide (FH) critically influences the sequestration of PO4 and organic matter (OM). While coatings of pre-sorbed OM block FH surfaces and decrease the PO4 adsorption capacity, little is known about how OM/Fe coprecipitation influences the PO4 adsorption. We aimed to determine the PO4 adsorption behaviors on humic acid (HA)-Fe coprecipitates in relation to surface and structural characteristics as affected by HA types and C/(C + Fe) ratios using the Fe and P X-ray absorption spectroscopy. With increasing C/(C + Fe) ratios, the indiscernible changes in the proportion of near-surface C for coprecipitates containing HA enriched in polar functional groups implied a relatively homogeneous distribution between C and Fe domains. Wherein PO4 adsorbed on FH dominated the P inventory on coprecipitates, yielding PO4 sorption properties nearly equivalent to that of pure FH. Structural disruptions of FH caused by highly associations with polar functional groups of HA enhanced the C solubilisation. While polar functional groups were limited, coprecipitates consisted of core FH with surface outgrowth of HA. Although surface-attached HA that was vulnerable to solubilisation provided alternatively sites for PO4 via ternary complex formation with Fe bridges, it also blocked FH surfaces, leading to a decrease in PO4 adsorption.

Magnetic behavior of metastable Fe films grown on Ir(1 1 1)

We investigated the growth of ultra-thin Fe films on Ir(1 1 1) by means of in situ low energy electron diffraction and spin-resolved photoemission techniques. We observe a (1 × 1) diffraction pattern, characteristic of the fcc substrate, below four monolayers (ML). Then, a complex superstructure starts to develop, compatible with the formation of bcc-like Fe domains aligned with the substrate according to the Kourdjumov–Sachs orientation relationships. The analysis of the diffraction patterns reveals a progressive evolution towards a fully relaxed bcc lattice, characteristic of bulk Fe. Both photoemission (filled states) and inverse photoemission (empty states) results show characteristic features related to the contribution of the Fe layer, evolving towards those observed on the Fe (1 1 0) bcc surface. Spin resolution allows to detect a spectral polarization above 4 ML, corresponding to the formation of bcc Fe, which gradually increases indicating the formation of an in-plane magnetized ferromagnetic layer in thick films. No in-plane net magnetization is detected in thinner films, independent of the sample temperature down to 30 K. Following recent investigations on the Fe/Ir(1 1 1) system with microscopy techniques, we link this observation to the stabilization of a non collinear spin structure yielding an overall nil magnetization.

A large deformation hybrid isogeometric-finite element method applied to cohesive interface contact/debonding

A hybrid NURBS-based isogeometric-finite element discretization technique is presented to take advantages of IGA for problems with regions demanding higher geometric accuracy or interpolation order. The validity of this coupled discretization is tested through standard patch test. Also, for demonstrative purposes, the proposed methodology is then applied to 2D interface contact/debonding of fiber–matrix as well as a 2D double cantilever beam peeling problem. Adopting a novel approach, the mortar method is used to account for both cohesive behavior and non-penetration constraint in the interface. Non-penetration constraint is enforced via Lagrange multiplier technique along with a mixed-mode cohesive law. The validity of the proposed unified contact/debonding formulation is tested against a contact/tension patch test. The stress contours after simulations show a smooth variation across IG and FE domains further demonstrating the coupling’s eligibility. Moreover, smooth contact pressure distributions are obtained along the interfaces resulting from higher-order NURBS basis functions. Having significantly less DOFs, the hybrid IG–FE discretization also behaved more robustly compared with linear FEs.

Stabilization of Natural Organic Matter by Short-Range-Order Iron Hydroxides.

Dissolved organic matter (DOM) is capable of modifying the surfaces of soil minerals (e.g., Fe hydroxides) or even forming stable co-precipitates with Fe(III) in a neutral environment. The DOM/Fe co-precipitation may alter biogeochemical carbon cycling in soils if the relatively mobile DOM is sorbed by soil minerals against leaching, runoff, and biodegradation. In this study, we aimed to determine the structural development of DOM/Fe co-precipitates in relation to changes in pH and C/(C + Fe) ratios using XRD, XPS, Fe K-edge XAS, FTIR, and C-NEXAFS techniques. The results showed that in the system with bulk C/(C + Fe) molar ratios ≤0.65, the ferrihydrite-like Fe domains were precipitated as the core and covered by the C shells. When the C/(C + Fe) molar ratio ranged between 0.71 and 0.89, the emerging Fe-C bonding suggested a more substantial association between Fe domains including edge- and corner-sharing FeO6 octahedra and DOM. With C/(C + Fe) bulk molar ratios ≥0.92, only corner-sharing FeO6 octahedra along with Fe-C bonding were found. The homogeneously distributed C and Fe domains caused the enhancement of Fe and C solubilization from co-precipitates. The C/(C + Fe) ratios dominated structural compositions and stabilities of C/Fe co-precipitates and may directly affect the Fe and C cycles in soils.

Product tunable behavior of carbon nanotubes-supported Ni–Fe catalysts for guaiacol hydrodeoxygenation

Bimetallic Ni–Fe nanoparticles supported on carbon nanotubes (CNTs) are prepared and evaluated for the catalytic hydrodeoxygenation (HDO) of a lignin-derived model compound guaiacol. Appropriate combination of Ni and Fe affords high activity and significantly enhances selectivity to cyclohexane or phenol, whereas monometallic Ni and Fe catalysts display poor activities or selectivities. The product tunable behavior of guaiacol HDO is found to be dependent on Ni/Fe atomic ratios. Cyclohexane and phenol are the major products over Ni5–Fe1/CNT with Ni/Fe atomic ratio at 5/1 and Ni1–Fe5/CNT with Ni/Fe atomic ratio at 1/5, respectively. Characterization results confirm that Ni–Fe alloys are formed and elicit synergistic effects on the HDO performance. The selectivity-switchable performance of Ni–Fe/CNT can be assigned to the synergism between Ni domains, where H2 can be easily activated, and Fe domains, which exhibited strong oxophilicity. The bimetallic catalysts give an enhanced stability without significant sintering of metal nanoparticles, while the monometallic catalysts show obvious deactivation due to the agglomeration of metal nanoparticles. Further results reveal that the conversion of guaiacol depends on not only the chemical state but also the size of the metallic nanoparticles. The catalysts with appropriate Ni/Fe atomic ratio and smaller particle perform better hydrogenolysis of C–O bonds, resulting in high selectivity to cyclohexane or phenol.

Ductile failure modeling and simulations using coupled FE–EFG approach

In the present work, a ductile fracture model has been employed to predict the failure of tensile specimen using coupled finite element–element free Galerkin (FE–EFG) approach. The fracture strain as a function of stress triaxiality has been evaluated by analyzing the notched tensile specimens. In the coupled approach, a small portion of the domain, where severe plastic deformation is expected, is modeled by EFG method whereas the rest of the domain is modeled by FEM to exploit the advantages of both the methods. A ramp function has been used in the interface region to maintain the continuity between FE and EFG domains. The nonlinear material behavior is modeled by von-Mises yield criterion and Hollomon’s power law. An implicit return mapping algorithm is employed for stress equilibrium in the plasticity model. The effect of geometric nonlinearity as a result of large deformation is captured by updated Lagrangian approach. The coupled approach is used to study the fracture behavior of two different cracked specimens in order to highlight its capabilities.

A coupled FE–EFG approach for modelling crack growth in ductile materials

AbstractIn this work, a coupled finite element–element free Galerkin approach has been used to model crack growth in ductile materials under monotonic and cyclic loads. In this approach, a small discontinuous domain near crack is modelled by EFG method, whereas the rest of the domain is modelled by FEM to exploit the advantages of both the methods. A ramp function has been used in the transition region to maintain the continuity between FE and EFG domains. Two plasticity models (GTN and von‐Mises) and three hardening rules (isotropic, kinematic and mixed) have been used to model the nonlinear material behaviour. Four different problems, i.e. single edge notched tension specimen, double edge notched tension specimen, compact tension specimen and three‐point bend specimen, are solved under plane strain condition using J–R curve approach. Finally, a CT specimen problem is also solved by coupled approach using three hardening rules and two plasticity models under cyclic loading.

Magnetic skin layer of NiO(100) probed by polarization-dependent spectromicroscopy

Using polarization-dependent x-ray photoemission electron microscopy, we have investigated the surface effects on antiferromagnetic (AFM) domain formation. Depth-resolved information obtained from our study indicates the presence of strain-induced surface AFM domains on some of the cleaved NiO(100) crystals, which are unusually thinner than bulk AFM domain wall widths (∼150 nm). Existence of such magnetic skin layer is substantiated by exchange-coupled ferromagnetic Fe domains in Fe/NiO(100), thereby evidencing the influence of this surface AFM domains on interfacial magnetic coupling. Our observations demonstrate a depth evolution of AFM structure in presence of induced surface strain, while the surface symmetry-breaking in absence of induced strain does not modify the bulk AFM domain structure. Realization of such thin surface AFM layer will provide better microscopic understanding of the exchange bias phenomena.