G.R. Kahler

Implementation of the Preisach-Stoner-Wohlfarth Classical Vector Model

A useful vector magnetic model must accurately simulate both the magnitude and direction of the magnetization when a magnetic medium is subjected to a linear or rotating applied field. Such a model has been recently presented as the Preisach-Stoner-Wohlfarth (PSW) model. The Preisach model computes the magnitude of the magnetization; the Stoner-Wohlfarth model computes the direction of the magnetization. These two models are combined into the PSW model. The PSW model is now initially implemented in a two-dimensional vector classical Preisach model. The model is computationally efficient since the magnetization angle is accessed for all applied fields from a single lookup table, which is generated by a one-time Stoner-Wohlfarth computation.

Modeling magnetic materials with the complete moving hysteresis model

Abstract The identification problem of the complete moving hysteresis model is discussed. It is shown that, although the formulation of the model is the same, the identification algorithms are different for medium-hard and soft magnetic materials. Parametric and non-parametric identification algorithms are discussed and analyzed. It is shown that parametric identification methods are experimentally much more accurate and robust than non-parametric methods.

Parameter identification of the complete-moving-hysteresis model for HTS steel

This paper discusses an extension to soft magnetic materials of the identification method of the CMH model which was originally introduced for medium hard magnetic materials. The proposed Preisach function for HTS steel, a soft magnetic material, is normal in the interaction field and is assumed to be lognormal in the critical field. Although the Preisach function is not symmetrical, the logarithm of the operative Preisach function is. However, the moving parameter, /spl alpha/, cannot be obtained by finding the value that removes this asymmetry because of the presence of apparent reversible magnetization and the lognormal nature of the Preisach function. All the Preisach parameters can be obtained using the major curve and the virgin curve only. For HTS steel, the squareness is 0.004, indicating a small irreversible magnetization component. The coercivity is 8.6 Oe; whereas the remanence coercivity is an order of magnitude larger, namely 123.5 Oe. >

Minimizing the deformation of a static magnetic field by the presence of a ferromagnetic body

Using boundary element methods, it is shown how linear and nonlinear single-valued, reversible magnetization of a body can deform a uniform magnetic field. Soft magnetic materials with a small amount of remanence were investigated. As the relative magnetic permeability of the linear magnetization of the materials increased, the deformation of the uniform magnetic field decreased because of the increase of the demagnetizing field. The deformation of the uniform field by nonlinear magnetization decreased with increasing impressed uniform fields. Use of a Preisach model will enable the evaluation of the impact of irreversible magnetization on the deformation of the uniform magnetic field and will enable methods to minimize this deformation. >

Field dependence of the barrier to magnetization reversal of a Stoner-Wohlfarth particle

It is well known that the energy barrier for magnetization reversal, EB, varies quadratically with the magnetic field for the Stoner-Wohlfarth model. However, the enthalpy H (switching energy) required to reverse the magnetization is the sum of EB and the work Wf done by the Neel fluctuation field. The sum of these two terms gives an enthalpy of reversal. If the fluctuation field is uniaxial and parallel to the holding field, then the enthalpy barrier for switching is linear in the holding field. The linearity is consistent with certain experimental results. If the fluctuation field is anisotropic, then for the same size field, the probability of the particle’s switching will depend upon the direction of that field. The paper discusses the holding field variation of the energy barrier for different fluctuation field directions.

Measured vector magnetization of magnetic particle tape

This paper presents two-dimensional vector measurements of major hysteresis loops of magnetic particle tape measured with a vibrating sample magnetometer. The measurements, presented in magnet and sample coordinates, may be used to evaluate how well the computations of a vector model fit the corresponding measured data. The measurement process is described, and the characteristics of the measurements are discussed.

Application of simplified vector Preisach model to vector magnetizing process

A series of measurements has shown that when a material is increasingly magnetized in a given direction, the magnetization perpendicular to this direction decreases to zero. A simplified vector Preisach model, an example of a coupled-hysteron model, has been introduced that incorporates this property into the vector model. In addition, this model satisfies the saturation property and the loss property. It can correctly compute scalar loops, since it is based upon the moving model, which properly corrects the congruency property; and it can incorporate the accommodation model and the aftereffect model to correct the deletion property. In three dimensions, the vector magnetization is computed from the integration of the product of a state vector, Q, and a Preisach function, p, both of which are defined in a six-dimensional Preisach space. The Qs are compared following selection rules determined by the applied field. This paper illustrates the calculation procedures for a complex magnetizing process. A material sample is subjected to a saturating field that is then reduced to zero. The field is then increased in an arbitrary direction while the vector magnetization is measured. Since the model parameters are only determined along the principal axes, the predictive capability of the model is thereby demonstrated. The predicted results of the model compare favorably to the results of experimental measurements.

Interpretation of thermal dependence of magnetic aftereffect for magnetic nanocomposite with slow decay rates

A new experimental characterization is presented of time-, field-, and temperature-dependent dynamic effects in magnetization of a nanocomposite which displays slow decay. Field and temperature variations of irreversible susceptibility, χ irr , decay coefficient, S, fluctuation field, hf , and activation volume, V, have been calculated for the nanocomposite sample (Co80Ni20) using a recently developed modified Preisach–Arrhenius (MPA) model. The sample is composed of non-interacting nanoparticles having negligible reversible magnetization. Non-Arrhenius behavior is observed in both the maximum decay coefficient, S max, and the fluctuation field, hf , as a function of temperature T. The peak of both temperature curves are identical and occur at a critical temperature Tk of ∼50 K, which agrees with our experimental results. Based on the effect of a temperature-dependent chemical potential on energy barrier, hf is studied for T < Tk and T ≥ Tk , respectively. A more complete MPA model that can predict the magnetization as function of time, field and temperature for a magnetic material with slow decay rates is proposed. This model uses a multi-variable analytical formula, , which incorporates the characteristic parameters.

Parameter estimation techniques for recording media

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.