Macroscopic Anisotropy Research Articles

Components of Magnetic Anisotropy of Soft Magnetic Nanocrystalline Fe-Based Films

We present quantitative evaluation results of micromagnetic structure parameters of nanocrystalline Fe, Fe95Zr5, Fe90N10, and Fe85Zr5N10films obtained by magnetron sputtering. It is shown that quantities of magnetocrystallineK1, magnetoelasticKME, magnetostaticKMS, and surfaceKa,Sanisotropies are components of experimentally measured effective local anisotropyKeff. The shape of the hysteresis loops of the films is determined by the presence of two main macroscopic effective magnetic anisotropies, one of which is the anisotropy field of stochastic domains, and the other is the magnetoelastic anisotropy field due to residual macrostresses.

Acoustic nonlinearity parameters for transversely isotropic polycrystalline materials.

This article considers polycrystalline materials with macroscopic elastic anisotropy and the effect of the anisotropy on the quadratic nonlinearity parameter used to describe second harmonic generation in solids. The polycrystal is assumed to have transversely isotropic elastic symmetry, which leads to a directional dependence of the nonlinearity parameters. Additionally, the anisotropy leads to second harmonic generation from an input shear wave. Estimates of the longitudinal and shear wave nonlinearity parameters are given as a function of single-crystal elastic constants, macroscopic anisotropy constants, and propagation direction. An inverse model is presented that relates measured nonlinearity parameters to the macroscopic anisotropy constants. The estimates of the nonlinearity parameters can be used to approximate the damage-free or baseline nonlinearity parameter of structural components, which helps the effort toward absolute measures of material damage.

In-situ investigation of the anisotropic mechanical behavior of rolled AA 7020-T6 alloy through lattice strain evolution during uniaxial tension

The texture-induced anisotropic mechanical behavior of a highly textured AA 7020-T6 (maximum orientation density of 29.7 multiple random distribution), was characterized by the lattice strain evolution along rolling direction (RD), 45° to RD and 90° to RD, respectively, under uniaxial tension using high energy X-ray diffraction. The uniaxial tensile tests were done till ultimate tensile strength (UTS), which show different yield strengths (YS), UTS and elongations along the three directions on a macroscopic level. On micromechanical level, the lattice strain evolution explains the correlation between crystallite orientation and different mechanical behavior, leading to the macroscopic anisotropy. In the elastic region, the sample 45° to RD has the lowest lattice plane dependent Young's modulus compared to the other two directions. In the elastic plastic transition region, lattice strain differences among different {hkl} lattice planes are highest for sample 45° to RD and lowest for sample 0° to RD. Moreover, the 45° to RD sample has the lowest lattice dependent YS. In the plastic region, the work hardening behavior of different {hkl} lattice planes in all three directions can be divided into two groups, corresponding to two types of dislocation combinations. However, {200} planes of samples 45° and 90° to RD behave abnormally due to the stress along <110> of the {200} planes and the orientation density of {200} planes parallel and perpendicular to the loading direction (LD).

Propagation and scattering of ultrasonic waves in polycrystals with arbitrary crystallite and macroscopic texture symmetries

A general ultrasonic attenuation model for a polycrystal with arbitrary macroscopic texture and triclinic ellipsoidal grains is described with proper accounting for the anisotropic Green’s function for the reference medium. The texture and the ellipsoidal grain frames in the model are independent and the wave propagation direction is arbitrary. The attenuation coefficients are obtained in the Born approximation accompanied by the Rayleigh and stochastic asymptotes. The scattering model displays statistical anisotropy due to two independent factors: (1) shape of the oriented grains and (2) preferred crystallographic orientation of the grains leading to macroscopic anisotropy of the homogenized reference medium. The model is applicable to most single phase polycrystalline materials that may occur as a result of thermomechanical manufacturing processes leading to different macrotextures and elongated-shaped grains. It predicts the strength of ultrasonic scattering and its dependence on frequency and propagation direction as a function of grain shape, grain crystallographic symmetry and macroscopic texture parameters and provides the texture-induced dependence of macroscopic ultrasonic velocity on propagation angle. It considers proper wave polarizations due to macroscopic anisotropy and scattering-induced transformations of waves with different polarizations. Competing effects of grain shape and texture on the attenuation are observed. In contrast to the macroscopically isotropic case, where in the stochastic regime the attenuation is highest in the direction of the longest ellipsoidal axis of the grain, the wave attenuation in the elongation direction may be suppressed or amplified by the texture with different effects on the quasilongitudinal and quasitransverse waves. The frequency behavior is also interestingly affected by texture: a hump in the total attenuation coefficient is found for the fast quasitransverse wave which is purely the result of macroscopic anisotropy and the existence of two quasitransverse waves; this hump is not observed in the macroscopically isotropic case. Striking differences of the texture effect on the directional dependences of the attenuation coefficients are found at low versus high frequencies.

Micromechanical modeling of stress-induced strain in polycrystalline Ni–Mn–Ga by directional solidification

Polycrystalline ferromagnetic shape memory alloy Ni–Mn–Ga produced by directional solidification possess unique properties. Its compressive stress–strain behaviors in loading–unloading cycle show nonlinear and anisotropic. Based on the self-consistent theory and thermodynamics principle, a micromechanical constitutive model of polycrystalline Ni–Mn–Ga by directional solidification is developed considering the generating mechanism of the macroscopic strain and anisotropy. Then, the stress induced strains at different angles to solidification direction are calculated, and the results agree well with the experimental data. The predictive curves of martensite Young’s modulus and macro reorientation strain in different directions are investigated. It may provide theoretical guidance for the design and use of ferromagnetic shape memory alloy.

Reversible gold nanorod alignment in mechano-responsive elastomers

Inspired by an increasing demand for stimuli-controlled assembly of nanostructures, mechano-responsive nanocomposites are designed with tremendous scope in material applications. Providing switchable properties by means of mechanical stimulation, elastomer-incorporated gold nanorods (AuNR) are presented herein. Stepless and reversible control over the orientational AuNR alignment – and therefore over macroscopic anisotropy – is exerted by uniaxial film elongation. In context of optical applications, substantial impact on the plasmonic properties within adjustable spectral ranges is demonstrated. Mechano-responsive nanocomposites with high thermal colloidal stability are prepared via a facile hetero-phase ligand exchange procedure where complete coverage of the AuNR surface with hydrophobic ligands is achieved.

Multiscale deep drawing analysis of dual-phase steels using grain cluster-based RGC scheme

Multiscale modelling and simulation play an important role in sheet metal forming analysis, since the overall material responses at macroscopic engineering scales, e.g. formability and anisotropy, are strongly influenced by microstructural properties, such as grain size and crystal orientations (texture). In the present report, multiscale analysis on deep drawing of dual-phase steels is performed using an efficient grain cluster-based homogenization scheme.The homogenization scheme, called relaxed grain cluster (RGC), is based on a generalization of the grain cluster concept, where a (representative) volume element consists of p × q × r (hexahedral) grains. In this scheme, variation of the strain or deformation of individual grains is taken into account through the, so-called, interface relaxation, which is formulated within an energy minimization framework. An interfacial penalty term is introduced into the energy minimization framework in order to account for the effects of grain boundaries.The grain cluster-based homogenization scheme has been implemented and incorporated into the advanced material simulation platform DAMASK, which purposes to bridge the macroscale boundary value problems associated with deep drawing analysis to the micromechanical constitutive law, e.g. crystal plasticity model. Standard Lankford anisotropy tests are performed to validate the model parameters prior to the deep drawing analysis. Model predictions for the deep drawing simulations are analyzed and compared to the corresponding experimental data. The result shows that the predictions of the model are in a very good agreement with the experimental measurement.

X-ray magnetic circular dichroism study of the magnetic anisotropy onTbMnO3

The magnetic anisotropy of $\mathrm{TbMn}{\mathrm{O}}_{3}$ was explored by means of polarized x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) measurements at the $\mathrm{Mn}\phantom{\rule{0.16em}{0ex}}{L}_{2,3}$ and $\mathrm{Tb}\phantom{\rule{0.16em}{0ex}}{M}_{4,5}$ edges as a function of temperature and magnetic-field intensity. The selective magnetometry measurements were compared with the macroscopic magnetic properties on single crystals. XMCD measurements at the $\mathrm{Tb}\phantom{\rule{0.16em}{0ex}}{M}_{4,5}$ edge as a function of the magnetic field reproduces quite well the macroscopic magnetic anisotropy at low temperatures with the Tb moments staying confined along their Ising axis within the $ab$ plane, whereas a weak XMCD signal is observed at the $\mathrm{Mn}\phantom{\rule{0.16em}{0ex}}{L}_{2,3}$ edge. These results point out that $\mathrm{T}{\mathrm{b}}^{3+}$ single-ion anisotropy is the only responsible for the magnetic anisotropy on this multiferroic compound at high magnetic fields. Moreover, we found $\mathrm{Mn}\phantom{\rule{0.16em}{0ex}}{L}_{2,3}$ XMCD measurements show that the cycloidal antiferromagnetic order is almost unaffected by the applied magnetic field at low temperatures under an applied magnetic field. Therefore, we discuss that this strong Ising nature of $\mathrm{T}{\mathrm{b}}^{3+}$ ions, through a magnetocrystalline coupling mediated by the oxygen atoms, must play an important role in the field-induced electric polarization flop and therefore in the magnetoelectric coupling on $\mathrm{TbMn}{\mathrm{O}}_{3}$.

Texture effect on mechanical properties anisotropy of products from Zr-based alloys

Technique of the macroscopic yield stress anisotropy calculation of Zr alloys based on texture f-parameters was validated in the frame of this work. In order to compare experimental and calculated anisotropy of products, samples cut out from rolled slabs of Zr- 1%Nb alloy along three directions (rolling, transversal and normal) were subjected to uniaxial tension and compression up to different deformation degrees. Investigation of texture evolution under loading was implemented by measuring of several direct pole figures by means of X-ray diffractometric methods for samples in the initial state as well as after their deformation. Using obtained texture data three normalized yield stresses for orthogonal directions of studied samples were estimated and compared with experimental values measured by initial loading curves.

Effect of hot working on the damping capacity and mechanical properties of AZ31 magnesium alloy

Magnesium alloys have received much attention for their lightweight and other excellent properties, such as low density, high specific strength, and good castability, for use in several industrial and commercial applications. However, both magnesium and its alloys show limited room-temperature formability owing to the limited number of slip systems associated with their hexagonal close-packed crystal structure. It is well known that crystallographic texture plays an important role in both plastic deformation and macroscopic anisotropy of magnesium alloys. Many authors have concentrated on improving the room- temperature formability of Mg alloys. However, despite having a lot of excellent properties in magnesium alloy, the study for various properties of magnesium alloy have not been clarified enough yet.Mg alloys are known to have a good damping capacity compared to other known metals and their alloys. Also, the damping properties of metals are generally recognized to be dependent on microstructural factors such as grain size and texture. However, there are very few studies on the relationship between the damping capacity and texture of Magnesium alloys. Therefore, in this study, specimens of the AZ31 magnesium alloy, were processed by hot working, and their texture and damping property investigated. A 60 mm × 60 mm × 40 mm rectangular plate was cut out by machining an ingot of AZ31 magnesium alloy (Mg-3Al-1Zn in mass%), and rolling was carried out at 673 K to a rolling reduction of 30%. Then, heat treatment was carried out at temperatures in the range of 573-723 K for durations in the range of 30-180 min. The samples were immediately quenched in oil after heat treatment to prevent any change in the microstructure. Texture was evaluated on the compression planes by the Schulz reflection method using nickel-filtered Cu Kα radiation. Electron backscatter diffraction measurements were conducted to observe the spatial distribution of various orientations. Specimens for damping capacity measurements were machined from the rolled specimen, to have a length of 120 mm, width of 20 mm, and thickness of 1 mm. The damping capacity was measured with a flexural internal friction measurement machine at room temperature. It was found that the damping capacity increases with both increasing heat-treatment temperature and time, due to grain growth and the increased pole densities of textures.

Grain Breakup During Elevated Temperature Deformation of an HCP Metal

AbstractA combination of mechanical testing, EBSD and crystal plasticity finite element modeling were used to investigate the influence of temperature on the fragmentation of grains in a zirconium alloy. The results demonstrate that grains of Zircaloy-4 fragment more as the temperature rises. This trend can be explained by an increasing difference between the CRSS values for 〈c+a〉 slip and 〈a〉 slip as temperature rises. This change in relative slip activities with temperature is supported by experimental observations of macroscopic anisotropy and in-grain misorientation axes calculated from EBSD data, as well as plasticity modeling. By tracking the microstructural evolution during deformation, it is shown that the two major texture components fragment to different degrees under the action of prismatic slip. Grains in the$$ \left\langle {11\overline{2} 0} \right\rangle $$112¯0fiber are significantly more stable than those in the$$ \left\langle {10\overline{1} 0} \right\rangle $$101¯0fiber, which break up. Grains of the latter fiber fragment heterogeneously as portions of the grain rotate in opposite directions, and some do not rotate at all.

Seismic wave propagation in anisotropic ice – Part 1: Elasticity tensor and derived quantities from ice-core properties

Abstract. A preferred orientation of the anisotropic ice crystals influences the viscosity of the ice bulk and the dynamic behaviour of glaciers and ice sheets. Knowledge about the distribution of crystal anisotropy is mainly provided by crystal orientation fabric (COF) data from ice cores. However, the developed anisotropic fabric influences not only the flow behaviour of ice but also the propagation of seismic waves. Two effects are important: (i) sudden changes in COF lead to englacial reflections, and (ii) the anisotropic fabric induces an angle dependency on the seismic velocities and, thus, recorded travel times. A framework is presented here to connect COF data from ice cores with the elasticity tensor to determine seismic velocities and reflection coefficients for cone and girdle fabrics. We connect the microscopic anisotropy of the crystals with the macroscopic anisotropy of the ice mass, observable with seismic methods. Elasticity tensors for different fabrics are calculated and used to investigate the influence of the anisotropic ice fabric on seismic velocities and reflection coefficients, englacially as well as for the ice–bed contact. Hence, it is possible to remotely determine the bulk ice anisotropy.

A macroscopic constitutive model of temperature-induced phase transition of polycrystalline Ni2MnGa by directional solidification

Directional solidification technology has been widely used to improve the properties of polycrystalline Ni2MnGa materials. Mechanical training can adjust the internal organizational structures of the materials, reduce the stress of twin boundaries motion, and then result in larger strain at lower outfield levels. In this paper, we test the microscopic structure of Ni2MnGa polycrystalline ferromagnetic shape memory alloy produced by directional solidification and compress it along two axes successively for mechanical training. The influences of pre-compressive stresses on the temperature-induced strains are analyzed. The macroscopic mechanical behaviors show anisotropy. According to the generating mechanism of the macroscopic strain, a three-dimensional constitutive model is established. Based on thermodynamic method, the kinetic equations of the martensitic transformation and inverse transformation are presented considering the driving force and energy dissipation. The prediction curves of temperature-induce strains along two different directions are investigated. And the results coincide well with the experiment data. It well explains the macroscopic anisotropy mechanical behaviors and fits for using in engineering.

Use of diffusion magnetic resonance imaging to correlate the developmental changes in grape berry tissue structure with water diffusion patterns.

BackgroundOver the course of grape berry development, the tissues of the berry undergo numerous morphological transformations in response to processes such as water and solute accumulation and cell division, growth and senescence. These transformations are expected to produce changes to the diffusion of water through these tissues detectable using diffusion magnetic resonance imaging (MRI). To assess this non-invasive technique diffusion was examined over the course of grape berry development, and in plant tissues with contrasting oil content.ResultsIn this study, the fruit of Vitis vinfera L. cv. Semillon at seven different stages of berry development, from four weeks post-anthesis to over-ripe, were imaged using diffusion tensor and transverse relaxation MRI acquisition protocols. Variations in diffusive motion between these stages of development were then linked to known events in the morphological development of the grape berry. Within the inner mesocarp of the berry, preferential directions of diffusion became increasingly apparent as immature berries increased in size and then declined as berries progressed through the ripening and senescence phases. Transverse relaxation images showed radial striation patterns throughout the sub-tissue, initiating at the septum and vascular systems located at the centre of the berry, and terminating at the boundary between the inner and outer mesocarp. This study confirms that these radial patterns are due to bands of cells of alternating width that extend across the inner mesocarp. Preferential directions of diffusion were also noted in young grape seed nucelli prior to their dehydration. These observations point towards a strong association between patterns of diffusion within grape berries and the underlying tissue structures across berry development. A diffusion tensor image of a post-harvest olive demonstrated that the technique is applicable to tissues with high oil content.ConclusionThis study demonstrates that diffusion MRI is a powerful and information rich technique for probing the internal microstructure of plant tissues. It was shown that macroscopic diffusion anisotropy patterns correlate with the microstructure of the major pericarp tissues of cv. Semillon grape berries, and that changes in grape berry tissue structure during berry development can be observed.

Magnetic Anisotropy in GeMnTe - ab initio Calculations

Recent magnetization and ferromagnetic resonance (FMR) measurements [1-4] show that in monocrystalline Ge1−xMnxTe layers grown on the BaF2 (111) substrate with x ≤ 0.1 the easy axis of magnetization is perpendicular to the layer. On the other hand, the usual in-plane easy axis due to dipolar interactions (shape anisotropy) is observed for polycrystalline and layered Ge1−xMnxTe with x ≥ 0.2. X-ray analysis suggests that the change of direction of the easy axis is connected with the change of crystal structure: the increase of the manganese content leads to change of the crystal symmetry from rhombohedral to cubic. Previous theoretical studies of anisotropy in semimagnetic semiconductors were based on the Zener model of ferromagnetism within effective–mass approach [5]. In the present work, first principles calculations of energy of magnetic anisotropy (EMA) in GeMnTe mixed crystals were performed using OpenMX package with fully relativistic pseudopotentials. The obtained results clearly indicate that EMA strongly depends on crystal structure, concentration of free holes and manganese content. The discussion of microscopic origin of magnetic anisotropy was conducted. The main conclusion is that the magnetic anisotropy is caused by interplay between spin – orbit and Coulomb interactions. The results show that the change of spin direction of manganese ions results in spatial redistribution of the electron charge. The discussion includes the differences between conducting and insulating cases, in particular the range of spin polarization caused by manganese ions. Finally, we point out the important role of chemical disorder on the macroscopic magnetic anisotropy.

Origin of the Current Transport Anisotropy in Epitaxial Graphene Grown on Vicinal 4H-SiC (0001) Surfaces

In this paper, the electronic transport in epitaxial graphene (EG) grown on the Si face of 8° off-axis 4H-SiC has been investigated, using both electrical characterization of macroscopic devices and conductive atomic force microscopy (CAFM). In particular, current measurements on linear transmission line model (TLM) structures with different orientations showed a current transport anisotropy related to steps orientation, with the resistance of EG in the direction orthogonal to the steps ~2× higher than in the parallel direction. Two dimensional morphology and current maps in EG over the stepped SiC surface were obtained by CAFM and revealed a local resistance increase of EG over the (11-2n) facets with respect to the (0001) basal planes. This effect allows to account for the observed macroscopic current transport anisotropy and can be explained in terms of a different interface nature between EG and SiC on the two faces, leading to a locally different substrate induced doping of EG.

Pore-scale analysis of electrical properties in thinly bedded rock using digital rock physics

We investigated the electrical properties of laminated rock consist of macro-porous layers and micro-porous layers based on digital rock technology. Due to the bedding effect and anisotropy, traditional Archie equations cannot well describe the electrical behavior of laminated rock. The RI-Sw curve of laminated rock shows a nonlinear relationship. The RI-Sw curve can be divided into two linear segments with different saturation exponent. Laminated sand-shale sequences and laminated sands of different porosity or grain size will yield macroscopic electrical anisotropy. Numerical simulation and theoretical analysis lead to the conclusion that electrical anisotropy coefficient of laminated rock is a strong function of water saturation. The function curve can be divided into three segments by the turning point. Therefore, the electrical behavior of laminated rock should be considered in oil exploration and development.

3D mapping of anisotropic ferroelectric/dielectric composites

Macroscopic anisotropy in polycrystalline materials is of key interest since it may help filling the gap between randomly oriented polycrystals like ceramics and single crystals. Non-destructive X-ray Computed Micro Tomography (XCMT) is a necessary step towards the full control and modelling of such anisotropy, beyond the standard scheme of interfaces. To ascertain this progress, XCMT is applied to 3D mixtures of ferroelectric and dielectric oxides processed by Spark Plasma Sintering (SPS). In such conditions, not only is this anisotropy seen in the overall dielectric parameters but it also shows up in ferroelectric properties. Experimental macroscopic parameters are linked to the 3D morphological anisotropy of individual MgO inclusions induced during SPS.

Effective surface anisotropy in polycrystalline ferromagnetic nanowires

Here we express the effective surface anisotropy for soft ferromagnetic nanowires as the function of the micro-structural behaviors. Many papers about these systems determine the reversal modes for the magnetization to explain magnetic properties of the nanowires. Our previous works related morphological structure with magnetic properties. The principal idea in this paper is to write the free magnetic energy for a soft magnetic cylindrical nanowire and make the comparison with our previous models. In this way we include the macroscopic effective anisotropy due to the disordered atoms and ignoring other microstructure terms related in our previous works. From this idea and our last model to these systems, we made an association that permit to express the effective anisotropy in function of the principal morphological characteristics of nanowires. The model is tested to determine the numerical value of the mentioned constant in Ni nanowires obtained by electrodeposition in porous anodic aluminum oxide membranes using the Transmission Electron Microscopy.

Reflection Phase Measurements for Ultrasonic NDE of Titanium Diffusion Bonds

The adoption of diffusion bonding in fracture critical titanium components has been limited by the complications that macroscopic anisotropy introduces to typical ultrasonic inspections. Previous attempts to overcome these limitations by using signal phase to extract otherwise hidden interface information showed promise but were susceptible to measurement error and proved impractical for typical aerospace component geometries. In the work presented here, significant improvements to the existing phase measurement approach are proposed alongside adaptations that permit its broader practical implementation. The principal parameters that affect the phase analysis of ultrasonic signals were investigated and their optimisation resulted in up to an order of magnitude improvement in phase measurement reliability, even at low signal-to-noise ratios. The application of these optimised parameters without a priori knowledge of the signal arrival time in an otherwise noisy waveform is illustrated, and the sensitivity of the approach to ambient temperature and annealing effects is also explored.