Parameters Of Domain Structure Research Articles

Surface microstructural design to improve mechanical and giant magneto-impedance properties of melt-extracted CoFe-based amorphous wires

The influence of surface microstructural regulation mechanisms on the mechanical and giant magneto-impedance (GMI) properties of as-cast melt-extracted CoFe-based wires has been systematically researched based on morphology, phase distribution and domain structure parameters. A series of statistical models were applied to analyze the mechanical properties and followed by mapping the curve of cumulative failure rate for wire application. It was found that the average and highest fracture strengths, average tensile strain increased with Cu substitution and reached peaks of ~3725 MPa, ~4250 MPa and ~2.7%, respectively. Verified structure-simulation experiments revealed that surface Rayleigh waves effectively split the main crack and the diffusely distributed nanocrystalline in surface area acted as a pinning point to impede the crack growth, enhancing the mechanical properties. The GMI ratio displayed similar variations and attained a maximum value of 700 ± 5% as well as the resistance and reactance ratios improved to ~687% and ~2206%, respectively. The enhanced relative dielectric permeability μs resulting from the increased domain wall energy density and the decreased surface domain width. The unique synchronous enhancement of CoFe-based wires satisfies the demand for emerging magnetoelectric sensor applications, e.g. flexible and wearable sensors, equipment self-monitoring sensors, and array robotic skin sensors under harsh working environments.

Nondestructive characterization of the domain structure of periodically poled lithium niobate crystal based on rigorous coupled-wave analysis

We report rigorous coupled-wave analysis (RCWA) method to non-destructively characterize the domain structure of periodically poled lithium niobate (PPLN) crystal. The strong light diffraction effect is achieved by applying a proper external voltage. We can observe reversed domain pattern and employ the detected diffraction intensity to optimally fit the result of RCWA based on least square method. Compared with conventional scalar diffraction theory, more accurate domain structure parameters with accuracies of 0.05 μm and 0.005 for the period and duty cycle are obtained respectively. It is proved that accurate, real-time and nondestructive characterization can be realized via this method. 1

Generation and detection of terahertz radiation by means of periodically and aperiodically poled crystals

The nonlinear optical methods for generating and detecting terahertz radiation using periodically and aperiodically poled crystals in the quasi-phase-matching mode are analyzed. Two radically different versions of optical pumping are considered: a quasi-continuous mode and pumping by Fourier-limited femto-second pulses. General relations are obtained, which determine the spectra of generated and detected waves through the optical pumping parameters and the crystal generator and crystal detector nonlinear transfer functions. It is shown that, by choosing the optimal spatial modulation of the crystal nonlinear susceptibility, one can control the shape of the generation and detection spectra. An optical scheme is proposed and the optimal parameters of domain structures for quasi-phase-matched generation and frequency-matched detection of forward and backward terahertz waves under quasi-continuous-wave optical pumping are reported.

Creation of Out-of-Plane Magnetization Ordering by Increasing the Repetitions Number $N$ in (Co/Au)$_{\rm N}$ Multilayers

The influence of the Co layer thickness as well as the number of repetitions N on the magnetic properties of (Co/Au)N multilayers was investigated systematically using magneto-optical techniques, vibrating sample magnetometry, and magnetic force microscopy. The studies focused on the characteristics of magnetic hysteresis loops in connection with magnetic domain structure parameters. Increasing the repetitions number, an out-of-plane magnetization ordering is created for Co layers with a thickness larger than the single-layer thickness at which the spin reorientation transition occurs.

A low-temperature neutron polarimeter for magnetic texture analysis

A miniature sample rotation device has been realized that fits into a cryostat of only 20 mm diameter and allows to perform a new procedure of aligning the anisotropy axis of uniaxially anisotropic ferromagnets precisely along the neutron beam, so as to derive the relevant domain structure parameters from the observed neutron depolarization. Test measurements on NdFeB samples of known orientation of anisotropy show the feasibility of this new method.

AFM characterization of domain structure of ferroelectric TGS crystals on a nanoscale

Atomic force microscopy has been used for the study of the surface topography and domain structures of triglycin sulfate (TGS) crystals. The images of various types of domains at the polar (0 1 0) surfaces of as-cleaved TGS crystals have been obtained (in contact mode and resonant mode). The crystals grown old, after annealing, γ-irradiated by various doses, were studied. It has been found that the surface relief of crystals after annealing differs from that of crystals grown old and irradiated: in the first case the peak-to-peak value is nearly constant whereas in the second case it varies in wide limits. The parameters of domain structure were determined. These parameters have been shown to be different for crystals grown old, crystals after annealing and irradiated crystals. It has been shown that, after cantilever scanning after a long period in different AFM modes the TGS surface experiences a partial polarization reversal.

Multilevel interaction between layers in layered film structures

An analysis was carried out of the mechanism underlying magnetic interlayer interaction in film structures. The investigation was based on the assumption that interlayer bonding affects film hysteresis. This was based on experimental data on the coercive force, the domain structure parameters, and the microstructure of Fe19Ni81/Cr/Fe19Ni81 and Fe15Co20Ni65/Cr/Fe15Co20Ni65 films. Theoretical estimates show that, as the thickness of the Cr interlayer increases, the exchange interaction between the ferromagnetic layers can be replaced by the magnetostatic interaction whose effectiveness is determined by surface irregularities and layer ‘magnetization ripples’.

Study of domain structure of thin magnetic films by polarised neutron reflectometry

A technique based on specular reflection of polarised neutrons, complemented by polarisation analysis and small-angle (diffuse) scattering under reflection has been suggested for determination of parameters of domain structure of thin (∼ 10–10 3nm) films. The generalised matrix formalism developed to cope with the problem of reflection of neutrons from layered magnetic media with magnetisation arbitrary in magnitude and direction allowed to describe the specular reflection from unmagnetised films. It has been shown that under total reflection the local (averaged over the region coherently illuminated by a neutron) magnetic induction, the mean (averaged over the sample) magnetic induction and the mean square direction cosines of the magnetic induction enter into the reflection and depolarisation matrices. It has also been shown that the first two Fourier transform coefficients of the angular distribution function of the domain magnetisation, connected with the mean magnetisation and magnetic texture, can be experimentally found. The study of magnetisation processes in Fe 36Co 64 (170 ± 3 nm) and Co (110 ± 3 nm) films demonstrates the possibilities of the new technique. The optical effect of averaging over the region coherently illuminated by a neutron, effectively leading to a decrease in the ‘local’ measured magnetic induction of the Co film, has been observed for the first time.

Magnetic domain structures of ferromagnetic thin films deposited on superconducting substrates (abstract)

The influence of superconducting substrates and coatings on the domain structure parameters of ferromagnetic thin films was analyzed, assuming validity of the London equation in the superconducting volumes (characterized by finite penetration depths) with standard boundary conditions. Analytic expressions for the demagnetization energy of arbitrary magnetization distribution were found by direct integration of the field Fourier components. This result was then applied both for strong in-plane anisotropy (N=E9el-type domain walls) and strong perpendicular anisotropy (Bloch-type walls). For the first case it was shown that superconducting substrate changes the domain structure properties only if the layer is also coated with superconducting material. Otherwise the parameters of domain structure change due to superconducting substrate, but the qualitative behavior remains the same. However, in the case of perpendicular anisotropy, essential changes in domains parameters appear even for normal capping. In thicker films the domain structure period is smaller than for the same film deposited on normal substrate. For sufficiently thin films the period becomes larger than for the normal substrate1 and increases to infinity at critical thickness L. Domains are fully suppressed, when the film thickness becomes smaller than L. The L value dependencies on different parameters of magnetic film and superconducting substrate were found by consideration of an isolated Bloch wall with finite width. This approach was also extended on finding the critical behavior of domain period. The results of numerical calculations, as well as analytic approximations, based on the derived formulas, are presented. It was shown that for films thinner than domain wall width the finite value can significantly influence domain structure parameters. Estimations made for typical values of superconducting and magnetic materials show that the critical thickness can exceed 100 Å.

Magnetic domain structures of ferromagnetic ultra-thin films deposited on superconducting substrates

The influence of bulk superconducting substrates and coatings on the domain structure parameters of a ferromagnetic ultra-thin film was analysed, assuming the validity of the London equation in the superconducting volumes. The problem was analysed for both easy plane and perpendicular easy axis films; however, as the effects of the superconducting substrate are relatively unimportant for films magnetized in plane, most of the article is devoted to easy axis films. Expressions for the demagnetization energy were found for arbitrary magnetization distribution. It was shown that a superconducting substrate changes the domain structure properties even if the layer is coated with a non-superconducting material. For sufficiently thin films the domain structure can be fully suppressed, which was shown by considering an isolated Bloch wall for larger anisotropy (Q > 1) and the critical domain structure for low anisotropy (Q < 1). The results of numerical calculations for critical ferromagnetic film thickness (as a function of anisotropy and London penetration depth) are presented.

Non-local elasticity of polydomain phases

In solid state phase transformations a single crystal or a grain of a polycrystal are often transformed into a regular system of structural domains which are differently oriented variants of the transformed phase. These domains appear as a result of the reduction in crystal symmetry caused by the transformation and are related to each other in a twin-like fashion. An assembly of plane-parallel twins forms a polysynthetic twin or polytwin.[1] Polytwins, in turn, may be parts of more complex hierarchical structures. Polysandwich structures of this kind are characteristic of many types of structural phase transli~rmations in solids, martensitic, ferroelastic, ordering and decomposition.[2] These polydomain structures arise in both first and second order phase transformations. If the polydomain region is embedded in an matrix, interactions between domains mediated by the matrix lead to the formation of an equilibrium polydomain structure corresponding to a minimum of the tree energy. Therefi~l'e, these domains have been termed elastic domains. If the characteristic length of the domain structure is small in comparison to the characteristic size of the solid, this homoor heterophase polydomain structure can be treated as a special type of polydomain phase with domain structure parameters as additional internal thermodynamical variables. These variables control the properties of the polydomain phase as well as the thermodynamics and kinetics of phase transformations to a considerable extent.

Domain structure of titanomagnetite grains with closure domains

Abstract Theoretical domain structure parameters and their temperature dependence have been calculated for 1–100-μm magnetite and intermediate titanomagnetite grains, on the basis of a simple model which incorporates closure domains. The model includes the effects of magneto elastic energy due to incompatible magnetostriction of main domains and closure domains and the reduction of magnetostatic energy of surface poles owing to the μ∗ effect. Refinements of the model incorporate the magneto elastic energy and the magnetostatic energy of domain walls. Grains in the form of cubes and rhombohedral prisms can be treated using the model. Comparison with analogous calculations for an open domain structure model reveals that the predicted magnitudes of domain width are significantly larger, by a factor of ∼ 5, for the closed domain structure model. The calculated domain widths are slightly greater for cubic grains than for grains with rhombohedral prismatic shape. The theoretical temperature variation for the closed domain structure model exhibits relatively stable domain structure at low to moderate temperatures, with an increase in domain width as the Curie temperature is approached, in contrast to the open domain structure model, which predicts a decrease in domain width at high temperatures, given realistic assumptions about the temperature dependence of the magnetostriction constant. The total magnetic free energy of the closed domain structure is substantially lower than that of the open domain structure, at all temperatures and for all grain sizes. This implies that closed domain structure should be preferred over open domain structure in magnetite and titanomagnetite. The theoretical predictions of domain width and its temperature dependence for the closed domain structure are in much better agreement with experimental observations than for the open domain structure.

Neutron depolarization in ferromagnets in terms of correlation functions

The change of the polarization vector of a monochromatic neutron beam after transmitting a ferromagnet can be described by a depolarization matrix. The contributions of different domain structure parameters to the depolarization can be obtained by considering neutron trajectories either passing a number of domains or passing a magnetization distribution described in terms of correlation functions. Both approaches are compared with each other and it is found that they deliver about the same results for ferromagnets composed by small domains. The method of analysing depolarization measurements in terms of domain structure parameters based on correlation functions is useful for ferromagnets close to magnetic saturation.

Domain structure in garnet films near the phase transition from the homogeneous state to the domain state

The influence of external magnetic field on the type and on the parameters of domain structure of garnet films near T N was studied. The magnetic field was applied perpendicular to the surface of epitaxial garnet films. It was found that the kind of observed phase transition from the homogeneous state to the domain state depends on the applied field intensity. The obtained results were compared with theoritical considerations of domain structure properties near T N in an external magnetic field.

Domin structure of (111) crystal plates of ferrite-garnets with uniaxial anisotropy

The influence of the magnetic field, thickness, and magnetic prehistory on the general form and quantitative parameters of domain structure (DS) of the (111) single-crystal plates of the ferrite-garnet (EuEr)3(FeGa)5O12 is investigated. The field interval of stability of circular (conical) and annular domains is determined. It is shown that the DS of ferrite-garnet structures with induced uniaxial anisotropy reveals a series of features which may be explained by the influence of cubic anisotropy.

Magnetooptical light concentration by regular domain structures

Expressions are obtained for the diffracted field in the Fresnel and Fraunhoffer diffraction domains. It is shown that the field in the diffraction pattern is the superposition of two orthogonally polarized fields. The distribution of a field with polarization orthogonal to the incident radiation depends substantially on the domain structure parameters. Thus, for zeros of the function f (ρ)=J0((π/Δ)ρ) assigned as radii of the annular domains, a magnetooptical light concentration in an annular image is possible, while for f(ρ)=cos(πρ2/2R12) the light is concentrated at a point, i.e., the annular domain structure plays the part of a lens. The effects of light concentration are examined for both the case of annular systems and strip domains.