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The analysis of magnetization oscillations (de Haas--van Alphen effect; dHvA effect) and features of the Fermi surface shape in three (3D)- and two-dimensional (2D) metals shows that the dynamic phenomena--the dynamics of domain walls and interphase boundaries during diamagnetic phase transitions--are described by a new nonlinear partial differential equation. The equation is a result of the inclusion of the case of multiple extremal cross sections of the Fermi surface in these metals. Our consideration indicates the possibility of the appearance of metastable non-spin domains (Condon domains) and first-order phase transitions to the ordered phase in the regime of dHvA oscillations for the two-frequency case. Sine-Gordon, Klein-Gordon, double sine-Gordon, time-dependent Ginzburg-Landau equations, and the telegraph equation are limiting cases of the derived equation. We show that particular moving kink-soliton solutions of the equation describe traveling wave fronts being moving domain walls and interphase boundaries in the Condon domain phase. Key words: nonlinear partial different equations, kink-soliton solutions, electron gas in quantizing magnetic fields, de Haas--van Alphen oscillations, Condon domains, diamagnetic phase transitions. L'analyse des oscillations de magnetisation (effet dHvA) et des caracteristiques de la forme de la surface de Fermi dans les metaux a 2D et 3D montre que les phenomenes dynamiques (la dynamique des murs de domaine et des frontieres d'interface pendant les transitions de phase diamagnetiques) sont decrits par une nouvelle equation differentielle partielle non lineaire. L'equation resulte de l'inclusion de sections efficaces extremes multiples de la surface de Fermi dans ces metaux. Notre examen indique la possibilite d'apparition de domaines non-spin metastables (domaines de Condon) et de transitions de phase du premier ordre vers la phase ordonnee dans le regime des oscillations dHvA pour le cas a deus frequences. Les equations de sine-Gordon, de Klein-Gordon, de double sine-Gordon, de Ginzburg-Landau dependante du temps et des telegraphes sont les cas limites de l'equation obtenue. Nous montrons que des solutions particulieres en soliton replie decrivent des fronts d'onde en mouvement qui sont des murs de domaine en mouvement et des frontieres d'interface dans le domaine de phase de Condon. [Traduit par la Redaction] Mots-cles : equation differentielle partielle non lineaire, solutions en soliton replie, gaz electronique dans la quantification les champs magnetiques, oscillations de Haas--van Alpen, domaines de Condon., 1. Introduction The occurrence and peculiarities of non-spin magnetic Condon domains in three-dimensional (3D) and two-dimensional (2D) nonmagnetic metals have been investigated for a half century [1-10]. Recent works have [...]

We provide a representation for the scaling limit of the d = 2 critical Ising magnetization field as a (conformal) random field by using Schramm--Loewner Evolution clusters and associated renormalized area measures. The renormalized areas are from the scaling limit of the critical Fortuin--Kasteleyn clusters and the random field is a convergent sum of the area measures with random signs. Extensions to off-critical scaling limits, to d = 3, and to Potts models are also considered. continuum scaling limit | critical |sing model | FK clusters | SLE | CLE

This paper shows that two apparently independent models of hysteresis--the Jiles-Atherton model, developed by Jiles and Atherton, and the energetic model, developed by Hauser--are mathematically equivalent. These two hysteresis models are examined with respect to their capability to describe the dependence of the magnetization on magnetic field and mechanical stress. Comparisons have been made between the predictions of the two models and measured hysteresis curves. Through a mathematical analysis of the structure of the models, conditions have been found under which both models predict the same magnetization curves. This 'common ground' agreement between the models has allowed us to establish correspondence between the descriptors of the models so that a mathematical transformation between the model parameters becomes possible. The result allows improved interpretation of the physical mechanisms that contribute to ferromagnetic hysteresis at different stages in the magnetization curve in terms of the reversible and irreversible physical processes such as domain wall motion and domain rotation which form the basis of these models. Furthermore, consideration of the internal demagnetizing factor has also allowed it to be included in the models. Index Terms--Anisotropy, demagnetizing factor, energetic model, hysteresis modeling, Jiles-Atherton model, mechanical stress.

This paper presents the comparison between two different numerical schemes for the analysis of switching phenomena in magnetic thin films. The first one is based on the finite-difference computation of the Landau--Lifshitz equation and on the magnetostatic field evaluation by fast Fourier transforms. The second one handles the spatial discretization of the Landau--Lifshitz equation by the edge finite-element method and solves the Poisson equation for the magnetostatic field with a hybrid finite element/boundary element technique. Index Terms--Finite-difference methods, finite-element methods, Landau--Lifshitz equation, magnetization reversal, thin films.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.04.025 Byline: Lon L. Hood (a), Nicola C. Richmond (a)(b), Keith P. Harrison (c), Robert J. Lillis (d) Keywords: Mars; Magnetic fields; Mars; interior; Mars; surface Abstract: Maps of the vector components of the martian crustal magnetic field over the strongly magnetized Terra Cimmeria/Sirenum region are constructed using Mars Global Surveyor magnetometer data. Although pronounced east-west trending anomalies are present on the radial and north field component maps at the mapping altitude ([approximately equal to]360-380 km), these trends are much less prominent at the lower aerobraking altitude ([approximately equal to]90-150 km). Comparisons with similar maps produced using artificial data at the aerobraking altitude indicate that elongated sources in this region may have maximum lengths along the martian surface of [approximately equal to]500 km and maximum aspect ratios of [approximately equal to]2. Iterative forward modeling of several relatively isolated anomalies in the mapped region yields paleomagnetic pole positions consistent with those estimated in previous studies of other anomalies using mapping phase and science phasing orbit data. On this basis, it is inferred that sources in the studied region are most probably magnetized primarily in northward or southward directions. Using this additional constraint, iterative forward modeling is then applied to determine a magnetization distribution that is consistent with data at both the aerobraking altitude and the mapping altitude. The model magnetization distribution, which includes 41 discrete sources, again indicates no highly elongated sources. An examination of surface geology in the region as well as a consideration of the global distribution of anomalies suggests that magmatic intrusions (e.g., subsurface dike swarms), cooling in the presence of water, are the most likely sources of the magnetic anomalies. Author Affiliation: (a) Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA (b) Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, USA (c) Southwest Research Institute, 1050 Walnut Street, Suite 400, Boulder, CO 80309, USA (d) Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA Article History: Received 30 November 2006; Revised 11 April 2007

Theoretical modeling of the magnetoelectric effect [ME.sub.E] for 2-2 connectivity composites is developed for three different boundary conditions by assuming perfect coupling at the interface. The calculated ME coefficients using the material properties of PZT and Terfenol-D are larger than those of any single phase ME materials.

In this paper, we propose a new approach to solve the magnetostatic inverse problem. The goal of the work is, from measurements of the magnetic field in the air, to rebuild a model for the magnetization of a ferromagnetic shell structure. It's then possible to calculate the field where sensors cannot be placed. This problem is usually ill posed or rank-deficient, it's then necessary to use mathematical regularizations. These techniques are based upon the injection of knowledge about the mathematical behavior of the solution. We preferred to add physical information. This solution allows us to get a faithful solution and to reduce significantly the number of sensors. Moreover, our method has been tested on a mock-up with real measurements and led to very promising results. Index Terms--Inverse problem, magnetization identification, magnetostatic, moments method, thin shell.

A formalism based on the perturbation theory, which permits for an analytical approximation to the solution of the micromagnetic equations, is presented. The approximation is applicable in the limit of small deviations of the magnetization from the uniformly magnetized state. These small deviations can lead to large effective anisotropy fields in magnetic elements, which can be large enough to dominate the spin reversal behavior.

An improved method for inverse shape optimization of magnetic devices using the Genetic Algorithms(GAs) with dynamically adjustable parameters is presented. The proposed method starts from an initial population using large number of bits per chromosome enabling searching for the optimal solution in a wider region without aggravating the computational speed. Later, as the optimization process evolves, the searching space is gradually decreased by restriction of the number of bits and by translation and reduction of the searching space according to the values of the objective function, therefore, dynamically adjusting to the best fit solution decreasing the computation resources to a minimum. The obtained results exhibit acceleration of the optimization process and increase of the solution accuracy. Index terms - Genetic algorithms, optimization methods, finite element methods, magnetic materials/devices, magnetization processes.

A model is derived to analyze the magnetization reversal mechanisms in small antiferromagnetic particles. Two magnetization reversal mechanisms are observed. In the first, the switching field reverses all spins in the particle and the magnetization relaxes to the opposite remanence following the removal of the applied field. In the second, particle magnetization disappears at a switching field which distorts the surface spin alignment and creates an opposite moment in the antiferromagnetic core of the particle.

High speed composite rotors typically require containment structures to protect personnel and equipment from high energy rotor material and fragments that result from rotor burst events, which may occur during rotor overspeed. Loading to the containment structure during a burst event is a function of rotor design and containment geometry. A containment system proposed by The University of Texas at Austin Center for Electromechanics uses graphite-reinforced composite cylinders to dissipate radial kinetic energy from the rotor debris and reduce torque loads transmitted to the rotor housing and mounting hardware. Using an analogous mass-spring-damper system, a model was developed with bond graph techniques to estimate containment loads and response. The bond graphs, state equations, and simulation results are compared with experimental results. The model is able to predict the general trends observed in experimental data and is used as a design tool for containment systems.

A hysteresis model is developed on the basis of a physical description of domain wall motion in magnetic materials. The mean behavior of a domain wall under the action of an external field is described by a simplified Preisach model. The superposition of several domain wall contributions to the average magnetization is treated by introducing a function describing the dependence of total domain wall surface on magnetization. The resulting model has a simple mathematical structure and permits a clear separation between irreversible processes responsible for energy losses and reversible ones. As distinctive mathematical properties, the model displays return point memory and a new kind of minor loop congruency. Theoretical predictions are compared with measurements on soft magnetic materials. Index Terms - Domain walls, hysteresis, Preisach model.

A brief discussion of the differences in two generalized slope models suitable for modeling metal evaporated tape is presented. The inclusion of idealized correlations between the sublayers in one of the models is proposed as an explanation for the differences in the predictions of these models. The correlations appear to mimic the effect of strong magnetic interactions that are thought to be present along the oblique easy-axis direction in metal evaporated (ME) tapes. Index Terms - Arbitrary easy-axis angle, metal evaporated tape, modeling of the recording process, multilayer Williams and Comstock model, slope model.

A simple phenomenological model is proposed for the nearly linear field-dependent strain and remanence in magnetic shape memory alloys. The model describes near saturation nonlinearities and shows that appreciable strain may result from phase-boundary motion. The model, however, fails to explain complexities involving Curie and martensitic temperatures and the influence of magnetization and strain.

The electromagnetic induction problem involving electrical anisotropy and magnetic anisotropy has been solved through the formulation of an analytical solution. This solution for a half-space anisotropic conductor has also been found applicable to electromagnetic induction problems in infinite plates and layered media. Meanwhile, an electromagnetic stress model is presented, which has the capacity to gauge magnetic field change under uniaxial stress.

A previously develop model for hysteretic loss and induced magnetization bridging was extended to include metallurgical bridges' inhomogeneous morphologies. The anisotropic continuum model presented a dimensionless parameter representing the area-fraction of bridged matrix material perpendicular to the filamentary axis. The parameters were then used to describe the bridging intensity.

Based on a multilayer approach, a generalized slope model is outlined for tape media with arbitrary magnetic layer thickness. A systematic study is performed which includes the role of demagnetization, angle dependence of the switching fields, switching field distribution, particle orientation, particle sizes, and geometric effects such as spacing between head and medium. The theoretical results are compared with experimental ones for high-density digital recording and yield excellent agreement between theory and experiment. Fundamentally, this type of lamina model is found to be incapable of treating magnetic screening effects correctly. In the case of metal evaporated (ME) tape with the easy axis tilted out of the film plane, this turns out to limit the usefulness of multilayer models for nonsaturation recording.

The effect of an external mechanical stress on the coercive force of Ni is different for bulk and for thin films. The bulk behavior is correctly explained by the Sablik-Jiles model which assumes that wall displacement is the driving mechanism of the magnetization process. In thin films, on the other hand, magnetization rotation might be a relevant mechanism, and this could explain the experimental differences with respect to bulk. In order to verify the correctness of this assumption, we constructed another model which was based on magnetization rotation. This new model is based on the bidimensional Stoner-Wohlfarth model, with additional terms which account for magnetostrictive energy and interactions among grains. Its predictions about coercive force behavior and general cycle shape are compared with experimental data on electroplated and evaporated Ni films with thicknesses from 15 to 200 nm. Index Terms - Hysteresis (magnetics), magnetic anisotropy, magnetization processes, magnetostriction, modeling, stress.

Spin valve and GMR read heads for ultra-high density storage applications are subject to strong self and inter-layer demagnetizing fields which dominate their behavior. A simple vector model for the description of the magnetic characteristics of macroscopic samples of spin valve material has been generalized and extended to describe finite width stripes by the incorporation of demagnetizing fields and intra-layer exchange coupling.

The demands of high density magnetic recording have motivated the development of vector Preisach models to supplant the scalar Preisach model. We present the details of such models, including methods for identification. The models are validated by the prediction of a variety of responses, including hysteresis loops, [Delta]M curves, and rotational behavior such as torque curves at intermediate field values. An application of the model to adjacent track interference is discussed.

Although Preisach models as originally proposed were phenomenological in nature, they can reveal physical insight into the magnetizing process if interpreted correctly. The classical model has been modified in order to achieve statistical stability, thus improving its predictive ability. The phenomena that these modifications explain include noncongruency of minor loops, accommodation, and rotational properties.

The effect of finite temperature T and observation time t on the Henkel plots of ac and thermally demagnetized systems has been investigated within the framework of a generalized Preisach model, in which it is assumed that thermally activated hopping will occur over all energy barriers W < [W.sup.*] = [k.sub.B]T ln(t/[[Tau].sub.0]), where [[Tau].sub.0] is a microscopic time, and will systematically drive the Preisach plane towards equilibrium. The Preisach distribution function is assumed to be a factorized product of a Gaussian coercive field distribution, with mean value [Mathematical Expression Omitted] and dispersion [[Sigma].sub.c], and a Gaussian interaction field distribution, with a self-consistent mean-field average [Mathematical Expresssion Omitted] and dispersion [[Sigma].sub.s]. Increases in temperature or observation time cause a progressive collapse of the hysteresis cycle, as expected, and also enhance demagnetizing-like curvature in Henkel plots, at least for ac demagnetized systems. An exception is a thermally demagnetized system with k = 0, which has a linear Henkel plot independent of [W.sup.*]. Varying the effective time for thermal relaxation of the magnetization from branch to branch of the hysteresis cycle can have the effect of imitating mean field interactions of both magnetizing-like and demagnetizing-like sign in systems with k = 0, and can even lead to Henkel plots which violate the lower boundary [i.sub.d] = -[i.sub.r].

Phenomenological micromagnetic and large-scale magnetization-dependent models of resistivity that produce giant magnetoresistance in granular multilayer magnetic thin films are described. Included in the models are intralayer and interlayer scattering components formulated explicitly in terms of the microstructural properties and characteristic transport lengths of the medium. The micromagnetic model provides insight into the influence of the magnetization distribution on the giant magnetoresistance response of the medium. The large-scale model which is derived from the micromagnetic model, is useful for obtaining media transport parameters from experimental data. Both models are used to study a set of annealed NiFe/Ag multilayer films.

For the design of a magnetoelastic device for force measurements in tendons of prestressed concrete structures, magnetic and magnetoelastic measurement data of the BH-normal induction curve were determined for three prestressing steel specimens using a NPL-permeameter. These data were compared to three saturation models known from the literature: the linear (LSL), the quadratic (QSL) and the square-root (RSL) saturation law. The LSI, which was found to be the most suitable of them, is magnetoelastically generalized to the extended linear saturation law (ELSL). The magnetoelastic magnetization data of three selected prestressing steel specimens agree well with the ELSL-model equation. Model parameters, mechanical data and chemical composition of the three specimens are given.

This paper presents a new method for determination of instantaneous magnetization characteristics of transformers (saturation and hysteresis loop) by taking into account only the rms values and no-load losses. This model is used to accurately study ferroresonance phenomena in a system of a cable-connected transformer.

The anisotropic and nonlinear behavior of doubly oriented and non-oriented sheets are modeled using the coenergy density. These models have been implemented in a finite element computation. A large generator has been modeled and the advantages of doubly oriented sheets compared to the conventional non-oriented ones are shown.

The properties of physically realistic scalar accommodation models are discussed using a new Preisach-based model. Such properties include the absence of accommodation in the major loop and the existence of a threshold field below which no accommodation occurs. Three types of accommodation processes are classified and discussed.

As a contribution to the development of methods for the design and the analysis of devices based on giant magnetostrictive materials, a model for the simulation of the dynamic behaviour of the nonlinear magnetoelastic medium is presented. The coupled magnetic, magnetoelastic and mechanical equations that describe the magnetostrictive problem are solved by means of the finite element method. The thin sheets bending principle (surface splines) is used to introduce in the simulation the nonlinear properties of giant magnetostrictive materials, obtained by static characterizations.

Using the complete-moving-hysteresis model it is shown that [Delta]m curves do not give a direct indication of the type of interaction but rather a combination of effects. An experimental analysis of commercial recording media shows that the model accurately computes various types of observed [Delta]m curves. It is shown that the measured asymmetry in [Delta]m curves can be attributed the reversible component of the magnetization.

A formulation for the FDTD treatment of partially magnetized ferrites is presented. It is based on the derivation of a system of time-domain differential equations from an empirical expression of the permeability tensor, normally used for designing microwave devices. This approach is applied to the full-wave analysis of waveguides loaded with partially magnetized ferrites.

To calculate nonlinear magnetostatics a new vector element in the volume integral equation has been developed. The magnetization vector in an element is expressed by using co- and contra-variant vectors corresponding to the each surface of the hexahedron element. To accelerate the conversion process, the iteration procedure has been divided into initialization and convergence parts. The method has been applied to TEAM workshop problem 13 of IEEE. Its calculated results agree with the measured data within 2%, indicating the method provides good accuracy.

A newly developed integral method for the static magnetic field analyses in shell structures is presented. The system matrix in weak form is symmetric and the magnetization i s represented by triangular vector finite elements preserving continuity of the normal components across element boundaries. The validity of this method is confirmed by calculating test shielding problems. The results by this method agree with the results by the finite element method and the analytical solution.

A new critical-state model for simulating magnetization of high temperature superconductors depends on the empirical fact that the decay of the critical current density does not depend on the field at large induction values. The model yields analytical expressions for the major magnetization loop shape and internal induction profiles. The critical current function includes a constant term and a field dependent Kim model type term.

A new model which includes the functions of coherent moment rotations helps elucidate the reversible magnetization process and its influence on magnetization curve of soft amorphous ribbons. Integration of the local magnetization effects on minimum energy condition and angular distribution yields the reversible I(H) curve. Application of the model to experimental I(H) recoil curves of positive and negative magnetostrictive ribbons indicates its agreement with theoretical concepts.

Computer simulation of the magnetizing process has been carried out by applying a numerical model to the theory of the rotation magnetization for magnetic materials. This model has been made in order to adjust to the two-dimensional magnetic property. This numerical model is combined with the finite element method in which the magnetic scalar potential and the magnetization are regarde as unknown quantities. It is possible to calculate that the magnetic materials with single domain structure are magnetized in the mode of rotation or of reverse of the magnetization vector.

A brief description of a magnetoelastic sensor is presented. The relationship between ac resonance and dc bias magnetization is explained. A 3D magnetostatic finite element model is used to describe the dc bias magnetization using either a uniform solenoidal or permanent magnet source. An analysis of the equation of motion of the magnetoelastic sensor is derived and an equivalent circuit model describing the ac resonance behavior is presented. The results of these models agree well with experimental data.

The modelling methods developed so far for grain-oriented electrical steels can not account for the true properties of materials. When these models were developed, more consideration was given to obtain fast convergence speed for numerical iterations than the accuracy of models themselves. For magnetic materials, the small changes in flux density B can cause dramatic change in permeability, so for the purpose of modelling devices, material modelling has t be as accurate as possible to reflect the true magnetic characteristics.