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Magnetic accommodation is observed in a rate-independent drift of minor loops towards a limit cycle. Several phenomenological models have been proposed that are not based upon physical reasons. Recently, two versions of physically based differential equation models were introduced. The differences between these two models are discussed here. Index Terms--Accommodation, hysteresis, physical modeling, Preisach modeling.

Magnetic bi-layers are becoming increasingly popular as a medium for perpendicular patterned media. In order to understand the net interactions between the layers and between adjacent magnetic elements in an array, we use a coupled Preisach model to model the hysteresis loops we measured for a sample consisting two magnetically soft layers of FeCoTaZr, separated by an 0.8-nm Ru spacer layer. The model reproduces the major hysteresis loop to decent agreement. The model was then decoupled to reveal the reversal behavior of the individual layers. This paper demonstrates that coupled Preisach modeling of the hysteresis loop is an effective tool to analyze such interacting material systems. Index Terms--Hysteresis modeling, patterned magnetic arrays, Preisach model, soft magnetic bi-layers.

We report on the first experimental demonstration of the details of the transient response in the four sequential processes of active magnetic regenerative refrigeration: magnetization, warm blow, demagnetization, and cold blow. The experimental results display the details of the gradual temperature divergence due to regeneration. The temperature change of the stationary solid bed is due to the magnetocaloric effect in a periodic field. The theory for the active magnetic regenerative refrigeration is applied to the transient processes in magnetocaloric regeneration. A time and spatial dependent model of temperature profile of the magnetization and demagnetization with thermal wave regenerative processes is developed. Index Terms--Magnetic refrigeration, magnetocaloric effect, transient magnetic regenerative process.

The Generalized Cobweb Method is presented as a technique to improve the accuracy and speed of calculations of the magnetization of hard magnetic materials that can be successfully described by means of the Preisach model. These calculations are usually carried out by a direct integration of the Preisach probability distribution over a certain area. However, this integration can be replaced by a faster and more accurate procedure based on the definition of a grid on the Preisach plane. The paper gives the steps to create these grids for a general probability distribution, and some details on how to use them to calculate the magnetization of the simulated system. Index Terms--Cobweb method, hard magnetic materials, hysteresis, Preisach model.

We use the differential equation method of computing the accommodation magnetization in a modified Preisach model. We present the properties of this model for a Gaussian medium, and show that the resulting model has neither the congruency property nor the deletion property. Index Terms--Accommodation, hysteresis, magnetic media, Preisach modeling.

Presents results of a numerical micromagnetic calculation for ferromagnetic fine particles. Discussion on the variation of coercivity and switching field; Comparison of the nucleation field with the Stoner-Wohlfarth model; Details of the equilibrium magnetization structures.

To make nanoparticles useful to fit various applications, the fundamental understanding of their magnetic and structural behavior is essential. A systematic in-depth study of the effect of field, temperature, and nanoparticles size on the critical points, and the magnetic properties of chemically synthesized Y2Fe17 nanoparticles have been performed. The blocking temperature varies with the change in the applied magnetic field as well as nanoparticles’ size variations. The Curie temperature was mostly influenced by particles’ size. Saturation magnetization and coercivity were shown to be temperature, size, and shape dependent. The results are significant and especially of interest in material science as they pave the path to a better understanding of different phenomena in nanomaterials in order for them to be used in diverse scientific applications. [ABSTRACT FROM AUTHOR]

A systematic study of the magnetocaloric effect of a Ni51Mn33.4In15.6 Heusler alloy converted to nanoparticles via high energy ball-milling technique in the temperature range of 270 to 310 K has been performed. The properties of the particles were characterized by x-ray diffraction, electron microscopy, and magnetometer techniques. Isothermal magnetic field variation of magnetization exhibits field hysteresis in bulk Ni51Mn33.4In15.6 alloy across the martensitic transition which significantly lessened in the nanoparticles. The magnetocaloric effects of the bulk and nanoparticle samples were measured both with direct method, through our state of the art direct test bed apparatus with controllability over the applied fields and temperatures, as well as an indirect method through Maxwell and thermodynamic equations. In direct measurements, nanoparticle sample’s critical temperature decreased by 6 K, but its magnetocaloric effect enhanced by 17% over the bulk counterpart. Additionally, when comparing the direct and indirect magnetocaloric curves, the direct method showed 14% less adiabatic temperature change in the bulk and 5% less adiabatic temperature change in the nanostructured sample. [ABSTRACT FROM AUTHOR]

A differential equation accommodation model, which we previously presented based upon the Preisach model, has been modified so that changing the accommodation constant, β, does not affect the major loop. This has the dual advantage that identification of the model parameters is easier and also ensures that an accommodating minor loop does not go outside the major loop. The modified model permits detailed comparison with experiment. There was a remarkable agreement between the model and previously published experimental data. [ABSTRACT FROM AUTHOR]

Unlike the case of an oscillating magnetic field, power losses in a magnetic material eventually start decreasing as the magnitude of a rotating field increases. In some hysteresis models, the loss increases monotonically as the magnitude of a rotating field increases. The simplified vector Preisach model and the reduced vector Preisach model do not suffer from this error. For magnetization-dependent reversible models, such as the Della Torre-Oti-Kadar, and for state-dependent models such as the complete moving model, the loss per cycle has two components. The first is computed from the Preisach integrals, and the second is computed from the change in the stored energy in the reversible component. It is noted that the latter loss can occur even if there are no Barkhausen jumps. This article discusses the details of how the model accomplishes this. [ABSTRACT FROM AUTHOR]

Nanocomposites have several advantages as a refrigerant for 100-300 K applications compared to the other common methods of assembling a magnetic refrigeration bed, such as a layered thermal bed, or mixing of different magnetic materials. This article discusses the thermodynamics and heat transfer analysis of an ideal and real active magnetic regenerative refrigeration cycle. An algorithm for the choice of optimum parameters is derived. [ABSTRACT FROM AUTHOR]

A proposed Preisach model for multilayer media previously presented accurately described first-order reversal curves as well as the major loop. The model used a moving Preisach model with graduated parameters for each layer in the media to account for the gradual loss of epitaxy of subsequent layers. A variable variance model was used to differentiate between major loop and reversal curve differences in curvature. The identification of parameters was complicated by their interaction, which made it difficult to fit all the data. This article suggests a technique for effectively reducing the interaction between the parameters, thereby simplifying the identification procedure. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The rate of magnetization change (magnetic after effect) which occurs after the magnetic field applied to a magnetic material is switched suddenly to a new value, is generally assumed to increase when the temperature is increased. Deviation from this temperature behavior, which has been observed in several cases, has been ascribed to changes in pertinent magnetic properties, such as magnetocrystalline anisotropy, activation volume, coercive field, etc., with temperature. We report here on the magnetic after effect temperature dependence of a magnetic recording material with magnetic properties that change very little with temperature over a wide temperature range but which, nevertheless, deviates considerably from a monotonic increase in decay rate with increasing temperature. We postulate that this behavior is explained by replacing the Maxwell–Boltzmann statistics by the Bose–Einstein statistics appropriate for the magnon energy distribution. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magneto-optical Kerr effect measurements performed on (0.3 nm Co/x Pt)[sub 15] multilayers with x=0.3–2.0 nm showed all samples to exhibit strong perpendicular magnetic anisotropy. Recent work has shown that for compositions near (0.3 nm Co/1.2 nm Pt)[sub 15], both polar Kerr rotation and ellipticity exhibit bimodal reversals in which the major hysteresis loops have two distinct field-dependent steps due to the contributions of two magnetic phases. To better understand this bimodal magnetization phenomenon, Kerr rotation and ellipticity were determined as a function of radial position from the center to the edge of this disk sample. These measurements exhibit a continuous variation from two-step (bimodal) behavior in the center to single-step (unimodal) behavior at the edge. Since these films were deposited via MBE with a heated substrate, it is believed that this phenomenon is related to thermally induced variations in interface effects such as alloying, abruptness, and morphology. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A systematic study of the size effect on the magnetic and structural properties of a Ni51Mn33.4In15.6 Heusler alloy converted to nanoparticles has been performed. We present new data to explain the enhanced magnetic properties of the nanostructured Heusler alloy synthesized through a high-energy ball-milling technique. The properties of the particles were characterized by X-ray diffraction, electron microscopy, and magnetometer techniques. Isothermal magnetic field variation of magnetization exhibits field hysteresis in bulk Ni51Mn33.4In15.6 alloy across the martensitic transition. As the size of the nanoparticles is reduced, there is an increase in the magnetization per unit of applied magnetic field, and a decrease in the coercivity as well as a substantial reduction in hysteresis. [ABSTRACT FROM PUBLISHER]

Reports on the characterization of minor loops using Preisach-based models. Description of the models; Analysis of hysteresis loops; State of hysterons in the classical Preisach model.

Describes a micromagnetic model that computes the vector magnetization in a three-dimensional geometry. Projection of a three-dimensional sample on an x-y plane; Analysis on the leakage of the magnetization out of the plane; Application of the model to study and optimize the flux conduction in a pipe.

Presents a study that examined the magnetic flux conductivity in the tip of a recording head for various applied field and closure domain configurations using a two-dimensional micromagnetic model to obtain the domain patterns in soft magnetic thin films. Magnetization process for small fields; Variation of the flux conduction for large fields; Relation of increasing field with the effective center of magnetic pole.

Part I. Presents a study that calculated the demagnetized state dependence of Henkel plots using the classical Preisach model. Description of the classical Preisach model; Models used to compute Henkel plots; Conclusions.

Presents information on a study that examined the nature of domain-wall motion coercivity in magnetic media. Numerical micromagnetic model used in the study; Temperature dependence of coercivity; Conclusions.

Deals with a study which determined the characteristics of the complete moving hysteresis model for the computation of magnetization. Information on Preisach function; Methodology of the study; Results and discussion.

Presents a study that proposed a moving-vector model of magnetic hysteresis that computes the media magnetization as the convolution of an applied-field-dependent vector with a Preisach distribution function. Function of pseudoparticles and Preisach models; Reason for the inadequacy of the vector properties of Preisach models; Relationship between points on the Preisach plane and Stoner-Wohlfarth asteroids.

Presents a study that discussed an algorithm to obtain a bilinear product Preisach function for magnetic hysteresis. Features of the product model; Details of the algorithm; Analysis of the accuracy of the algorithm.

Discusses a study which employed the moving model modification to generalize the vector Preisach model. Details of the classical Preisach function; Information on the ellipsoidally magnetizable media; Experimental determination of the Preisach function.

Focuses on a study that calculated Henkel plots using a hysteresis model base on independently moving domain walls. Background on Henkel plots; Computational procedure used; Results and discussion.

Presents an experimental verification of a vector moving Preisach model used to describe partially oriented particulate media by pseudoparticles. Description of the model considered in the study; Measurement of the angular dependence of the magnetic properties using a vibrating sample magnetometer; Comparison of the experimental results with the orientation dependence of the squareness and coercivity.

Deals with a study that illustrated a solution for a scalar bivariate moving model for the case where the Preisach function is Gaussian with equal standard deviations in the two directions. Open question important in the analysis of hysteretic materials using Preisach techniques; Description of magnetization-dependent models; Basic assumption of the product model.

Presents a study that developed a modular computer package to obtain the behavior of the components of the magnetization of media models as an applied field's strength is varied and rotated. Function and description of the package; Reason that the model was intended to be used to find an optimum set of model parameters; Remanent magnetization curve along the x axis for the models.

A model for the vector magnetization of a distribution of uniaxial particles is presented. Recent work by the authors decomposed the magnetization into two components and modeled the total vector magnetization as their vector sum. Anisotropy could be ideally modeled as a constant field, but this leads to a model of unidirectional anisotropy. Considering uniaxial media, such approach will only be valid for small angles. Hence, in this paper, a model is proposed that calculates the total magnetization of a distribution of uniaxial particles as the vector sum of irreversible and reversible components. The magnitude of the irreversible component is modeled using a Preisach differential-equation approach; however, other valid models can be used. The direction of the reversible component is modeled using the minimum energy approach of the classical Stoner–Wohlfarth model. The final result of the model is an unsymmetrical lag-angle plot for intermediate applied field values, which is consistent with the measurements. [ABSTRACT FROM PUBLISHER]