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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.

A fast differential equation approach for the Della Torre, Oti, and Kadar model has been extented to the complete moving hysteresis (CMH) model. Also, a cobweb technique for calculating the CMH model is also presented. The two techniques are contrasted from the point of view of flexibility and computation time. Index Terms--Cobweb, complete moving hysteresis model, hysteresis, magnetic modeling, Preisach model.

Two methods of mode pushing are compared. The newer method, Automatic pushing, uses energy minimization to relocate a wall, as one entity. The older method, Adaptive mode pushing, uses the reversal of the direction of motion of the wall to determine when to end the mode pushing. It is seen that automatic pushing is comparable and often speeds up the calculation significantly more than adaptive mode pushing. Index terms - Micromagnetics, convergence, domain wall, inclusion

A Preisach based magnetization model is presented to work specifically on highly magnetostrictive materials. The model accounts for the additional anisotropy introduced when a prestress is used to activate the high strain, by using a bimodal structure. The necessity of strain feedback to deal with the magneto-mechanical effect is discussed for Terfenol-D specifically. The model is based on a fast implementation of the DOK magnetization model, so it is suitable for real time control applications. Index terms - magnetostriction, Preisach, bimodal, Terfenol.

Although scalar Preisach models have been increasingly accurate and efficient in describing material behavior, vector models, necessary to quantize complex magnetizing processes. are not as well developed. This paper presents a coupled vector model where the coupling is performed by a set of selection rules, after which the individual components can be calculated independently. This model reduces to a scalar model under appropriate conditions and the identification of its parameters is very straightforward. Index Terms - Accommodation, hysteresis Preisach modeling, magnetic viscosity, vector models.

The solution of micromagnetic problems using finite difference techniques is complicated by the presence of stiff modes. Effective techniques have been developed to handle them if they can be identified. This paper presents a technique for identifying them and discusses how to accelerate their convergence. This technique can also be used to classify the solutions once they have been achieved.

Increasingly accurate models have been derived from physical principles whose parameters can be easily measured using computer controlled VSMs. This paper shows that, although recording industry parameters are not adequate to completely characterize media, their values are derivable from the parameters of these models.

Experiments have shown that even for very thin laminations, there is an appreciable eddy current effect for high recording frequencies. A technique is suggested here for including these effects in a micromagnetic calculation. This technique has been implemented in a finite difference calculation and some results are presented. The structure of the computational algorithm is considerably different from conventional eddy current calculations.

In materials with large magnetic moments, the interaction field can be sufficiently large so that the Preisach function has a significant contribution outside the fourth quadrant of the Preisach plane. It is shown that such media, even a perfectly aligned medium that has an apparent reversible component, will have nonzero squareness. In this case, one has to distinguish between remanence and the irreversible component of the magnetization. Since measurements cannot distinguish between the two effects, the procedure for the identification of model parameters must model the effects and use their different properties in order to separate them. This paper discusses such an identification procedure. Index Terms - Electromagnetic measurements, hysteresis (magnetics), nonlinear magnetics, parameter estimation.

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.

As recording heads become smaller to achieve higher recording densities, their domain structure increasingly influences their performance. Due to the presence of closure domains in the head, for track widths the order of 1 [[micro]meter], the available head flux becomes limited and the asymmetry in the flux geometry is increased. To study the problem, this paper presents some micromagnetic calculations on thin-film recording heads. The model computes the domain variations in the head when a field is applied for both permalloy and iron-nitride. It is found that the flux asymmetry is small for small fields, increases to a maximum, and finally disappears at saturation. Possible designs that could reduce this effect are discussed.

The effects of the domain structure in the write head on a recording track are modeled by studying the magnetic field distribution generated by a thin film inductive head such as those used in high density recording on hard disks. The magnetic field around the head gap is calculated in three dimensions from a magnetization configuration generated by a two-dimensional micromagnetic model. Domain variations inside the recording head produce asymmetries in the recording track due to the presence of closure domains in the head. The effects of this asymmetry on overwrite are discussed.

Numerically efficient Preisach-based vector hysteresis models for ellipsoidally magnetizable media are presented. Both models are based on orthogonal coupled scalar models and take into consideration the variation in particle switching fields and interaction; however, the coupling mechanism is different in the two models. The rules determining the magnetization state corresponding to the vector applied field are discussed. The basic rotational remanence properties of the models are compatible with observed vector phenomena.

This paper presents the relationship between the various Preisach-based scalar hysteresis models. The statistics of the interaction field computed by these models, the hierarchy of these models, and the corresponding parametric identification techniques are discussed. This enables the design engineer to determine which of the models provides sufficient detail, yet is simple enough, to characterize the aspect of hysteresis that is of particular interest.

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.

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 statistical interpretation of the Preisach model led to the moving model that relaxed the congruency property and to the complete moving hysteresis model (CMH) which included a state-dependent locally-reversible magnetization. Since, like all Preisach models, these models possess the deletion property, minor hysteresis loops calculated by them are immediately stable. In real media successive traversals of minor loops are not superimposed. Accommodation describes this approach to equilibrium of static minor hysteresis loops, which may require many cycles for some materials. This paper presents a further statistical modification to the Preisach model to include accommodation, and it discusses the properties of such a model and the identification of its parameters.

The theory of identification of Preisach parameters has been applied to two types of magnetic recording tapes along the easy and hard directions. The metal evaporated (ME) tape along the hard axis is identified as a three-quadrant medium. The implications for understanding the position of the maximum magnetic aftereffect decay rate are discussed. Index Terms - coercivity, Preisach model, remanence, three quadrant medium

Aftereffect has been understood qualitatively since Preisach first reported it and Neel and Wohlfarth explained its origin. We use the Preisach model to quantitatively discuss relaxation of magnetic materials as a function of their history over the entire time regime. The maximum decay rate occurs at the average operative critical field only for single-quadrant media with small fluctuating fields. Index terms - Arrhenius law, decay parameter, magnetic aftereffect, Preisach model.

An experimental vector analysis of the rotational magnetization, remanent magnetization and reversible magnetization properties of longitudinal recording samples is presented. It is found that for large fields the locus of the magnetization vector, the remanent magnetization vector and the reversible magnetization are all ellipses whose aspect ratios are fundamentally different. For smaller rotating fields, the trajectory of the magnetization vector and the remanent magnetization vector are spirals whose limit cycle is an ellipse; however, the reversible magnetization vector is an ellipse. These experimental results are in agreement with a recently proposed vector hysteresis model for recording media.

Aftereffect and accommodation are measured in metal recording media rising either evaporated cobalt (ME) or particulate iron (MP) as the magnetic material. These materials are highly anisotropic and measurements have been made parallel to the plane of the media both along the easy direction and along the hard direction. Along the easy direction, the loops are square and there is only a small difference between the coercive field, [H.sub.c], and the remanent coercive field, [H.sub.ci]. Along the hard direction the squareness is approximately one-half that along the easy axis and [H.sub.ci] is shifted considerably from [H.sub.c].

The concept of performing micromagnetic calculations is suggested in which some of the calculation points are repositioned according to energy considerations. In this way the stiffness of the problem can be reduced.

This paper contrasts the experimental applicability of the sequential parametric identification method with the traditional curve fitting parametric identification method. Both methods yield similarly good results in computing some magnetization curves; however, the sequential method gives results that are significantly more accurate in predicting experimental curves.

This paper illustrates the use of the dynamic Preisach model with accommodation in calculating the remanence after the application of two pulses. The DOK model is used to calculate the state-dependent locally reversible magnetization.

The paper analyzes the anomalous behavior of the magnetic aftereffect decay coefficient with temperature, which has been established experimentally from a thermodynamic point of view. The Arrhenius law, which has often been used to model magnetic aftereffect, is based on the Maxwell-Boltzmann (MB) statistics. At low temperatures, however, magnons obey Bose-Einstein (BE) statistics, which have a different energy spectrum. MB statistics are a good approximation to BE statistics in the temperature range in which most devices operate. The variation in temperature, governed by chemical potential that is essentially linear, has a negative slope and is zero below a low but finite temperature. Other explanations for this anomalous behavior would predict an incorrect type of temperature dependence. This new interpretation of magnetic aftereffect may have profound implications on accelerated testing to determine life expectancy of recordings. Index Terms--Accelerated testing, chemical potential, magnetic aftereffect, quantum statistics.

We present a useful technique to calculate the magnetic response of hard magnetic materials to the application of magnetic fields. We consider that these materials can be described by means of Preisach-based models and the parameters defining the material are distributed according to a Gaussian function. We find that the utilization of a grid in a 'cobweb' style can help us to improve both accuracy and speed for this kind of simulations. We show the usefulness of this grid by solving in an easy way inverse type problems. Index Terms--Cobweb grid, hard magnetic materials, hysteresis modeling Preisach models.

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]