Moving Preisach Model Research Articles

Preisach analysis of sputtered SmCo thick films

Here, we present an implementation of the moving Preisach model to describe the magnetic behaviour of Sm-Co films. We use two independent Preisach distributions to separate the magnetization into reversible and irreversible components. The numerical simulation works very well for a system where two magnetic phases are weakly or negligibility coupled. We tested our implementation on nanocrystalline Sm-Co films prepared by sputtering and having composition around Sm25Co75. We found that the Sm25Co75 film has a soft and hard phase and quantified their contributions to the total magnetization. Using the moving Preisach model, we characterized the properties of the hard phase, which has a coercivity of 1.26 T and contribution of 74% to the total magnetization. The soft magnetic phase contributes 26% to the total magnetization and has a coercivity of 0.056 T.

Implementation procedure for the generalized moving Preisach model based on a first order reversal curve diagram

First order reversal curves (FORC) of nanocomposite Nd2Fe14B/Fe3B magnetic materials were measured to attain a FORC diagram, which characterizes reversible magnetization, irreversible magnetization, and magnetic interactions in a hysteresis system. Then, generalized moving Preisach model (GMPM) was implemented based on the FORC diagram. Reversible and irreversible magnetizations shown in FORCs and a FORC diagram were used as an input of GMPM. Coupling interaction between reversible and irreversible magnetizations was added when calculating reversible magnetization. Meanwhile, irreversible magnetic moments’ interaction was approximately represented by mean field interaction. The result shows that the simulated main curves mostly coincide with the experimental curves.

Magnetostatic Interactions and Coercivities of Ferromagnetic Soft Nanowires in Uniform Length Arrays

First-order reversal curve diagrams have been used to investigate magnetostatic interactions and average coercivity of individual wires in soft ferromagnetic uniform length nanowire arrays. We present a method for identifying these physical parameters on the out-of-plane first-order reversal curve diagrams: the position of the irreversible part on the critical axis is a good approximation to the average value of the nanowire coercivity and the maximum interaction field is equal to the interaction field at saturation. Their dependence upon material (CoFeB and Ni) and nanowire length are presented. The magnetostatic interactions increase linearly with length, in agreement with a model developed previously. The global array coercivity, obtained from magnetization curves, is generally lower than the apparent average coercivity for individual nanowires. This coercivity reduction increases linearly with the magnetostatic interactions. The general shape of the out-of-plane first-order reversal curve diagrams is compared with those obtained from a theoretical moving Preisach model.

Application of a Preisach-type hysteresis model to the magnetic evaluation of material degradation

Preisach-based magnetic characterization is applied as a non-destructive method to evaluate material degradation due to metal fatigue. At predetermined interruptions of the cyclic mechanical loading a set of first order symmetric and a set of second order minor magnetisation loops are measured and analysed using both the classical and the moving Preisach model. The evolution of microstructure dependent magnetic features such as the Preisach distribution function, the mean-field parameter k and the local coercive field distribution Qc(hc) is monitored: k increases and the peak value of Qc decreases with the number of stress cycles. Moreover, for both parameters the rate of change is higher during the last 10% of the fatigue lifetime.

Magnetoelastic behavior of ferromagnetic materials using stress dependent Preisach model based on continuum theory

The magnetic and the mechanical constitutive equations are proposed on the basis of the continuum theory of magnetoelastic materials. The rate type expression is derived from the moving Preisach model by taking into account the stress dependence as the magnetic constitutive equation. From the symmetry of the constitutive equations, it is shown that the stress magnetization effect can be derived from the stress-dependent magnetization and magnetostriction curves. It is experimentally confirmed that the constitutive equations can describe typical magnetoelastic behaviors of a ferromagnetic material such as the magnetization and the magnetostriction curves under the stress and the stress magnetization curve.

Temperature dependent integral generalized Delta-M plots and interactions in cobalt nanoparticle systems

The effect of inter-particle interaction in samples of Co nanoparticles dispersed in different volume fractions in a wax matrix was studied. The evolution of interaction intensity in the Co nanoparticle systems as a function of temperature was determined by measuring the integral generalized Delta-M curves. These experimental curves do not require AC demagnetized states of the sample, which is an important simplification of the experimental procedure. The results are analyzed with a generalized moving Preisach model.

The use of generalized Δ M plots in the magnetic characterization of particulate media

We present here the properties of the generalized and the integral generalized Δ M plots which are used to build an identification algorithm for the Generalized Moving Preisach Model. We also simulated systems of interacting particles with magnetic moments dynamics described by the Landau–Lifshitz–Gilbert equation. In each equilibrium state one studies the statistics of the interactions and other relevant parameters. These parameters are compared with the ones provided by the identification algorithm.

Study of grain interactions in longitudinal hard disk media

The magnetization processes for a set of two samples of hard disk media were interpreted in the frame of a non-relaxing, scalar, generalized moving Preisach model. A satisfactory fit was obtained using a Gauss distribution of interaction fields and a Gumbel-type distribution of coercivities. The integral generalized Δ M plot was used for confirming the reliability of the obtained Preisach parameters. For the investigated samples, the grain interactions have a mean-field character.

An analytical method for the identification of the Preisach distribution function

The paper presents an analytical computation of the factorised distribution function in moving Preisach model starting from a set of measured symmetrical loops. The obtained solution is simple and computationally fast if compared with numerical algorithms usually employed. The proposed method is applied to a procedure for the identification of a NO FeSi alloy including the mean-field terms.

Interaction evaluation in particulate media using the integral generalized ΔM plot

This paper presents a method of estimating the parameters of the generalized moving Preisach model by simple dc measurements. Two points on the integral generalized ΔM (IGDM) plot are used, which are very sensitive to choice of the parameters describing the interactions. The technique allows a refinement of parameters once that the coercive field distribution is approximated by using the magnetic hysteresis loop (MHL), dc magnetization curve (DCD), and the isothermal remanent magnetization curve starting from the dc demagnetized state of the system (IRMdc). The method may also be used to test the parameters provided by different identification techniques by considering the two points on the IGDM curve as check points for the simulations.

Automatic parameter identification for the multilayer media Preisach model

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.

Preisach analysis of epitaxial hard/soft bilayers

We used the moving Preisach model to study the magnetization-reversal process in epitaxial SmCo (1 1 ̄ 0 0) /Fe bilayers prepared by magnetron sputtering. The SmCo(20 nm)/Fe( t nm) ( t=0, 5, 10, 20) bilayers were grown onto single-crystal (1 1 0)MgO substrates with an epitaxial 20 nm Cr(2 1 1) buffer layer. The second-quadrant magnetization curves were strictly reversible up to a field H 0, close to the field H c at which the magnetization switched irreversibly. Henkel plots for these bilayers indicated very strong magnetizing interactions for all films. Magnetization reversal in these films reflects their epitaxial structure.

Micromagnetic evaluation of statistical and mean-field interactions in particulate ferromagnetic media

Samples with Stoner–Wohlfarth ferromagnetic particles interacting only through dipolar magnetostatic fields were computer generated and the effects of the interactions on the magnetisation processes have been analysed. In some geometrical configurations of the particles, magnetostatic mean-field interaction field was also obtained, in agreement with the usual assumption in the moving Preisach model. A micromagnetic analysis of the magnetostatic mean interaction field is made. Classical Δ M and integral generalised Δ M curves have been calculated and the results have been analysed.

Interparticle interactions in magnetic recording media as obtained from high-order measurements by a Preisach model

Generalized ΔM plots, which allow interactions to be investigated for any starting remanence state, have been used in the analysis of interactions in particulate magnetic recording media for three samples [very high speed (VHS) videotape, Ba-ferrite dispersed particles oriented and nonoriented]. The results have been interpreted using a generalized moving Preisach model. This gives a good fit to the hysteresis loops and ΔM plots. However, agreement with the generalized ΔM plots is less complete. This is interpreted in terms of a requirement for a magnetization dependent standard deviation in the generalized moving Preisach model.

Comparision of simulated and measured magnetisation curves using a rigorously identified moving Preisach model

The consequent identification of the Preisach function requires a knowledge of the correct hypothetical field, allowing the transformation of measured first-order reversal curves from external to internal field dependencies. In the present paper we discuss the difficulties we met during the application of theoretically correct algorithm to soft magnetic materials with Preisach function concentrated near macroscopic coercivity and with relatively low non-congruency.

Study of reversible and irreversible magnetization processes of coprecipitated cobalt ferrite

Cobalt ferrite was obtained by coprecipitation of iron and cobalt sulphates into acetone medium. The Co0.62+Fe0.43+[Co0.42+Fe1.63+]O4 cation distribution was obtained from Mössbauer spectroscopy at room temperature. Saturation magnetization of 74.1 emu/g and an intrinsic coercive field of 528 Oe were measured using a vibrating sample magnetometer. Using the moving Preisach model, separation of reversible (Mrev) and irreversible (Mirr) magnetization components was performed. The parameters η defined as η=(dMrev/dMirr)Hi and km the moving Preisach parameter expressed through the relation η=kmχrev, were evaluated in order to investigate the hysteretic behavior of Mrev. Additional characterization was done in order to investigate the elemental composition, structure, and morphology of the samples.

Preisach analysis of reversible magnetization in SmCo/Fe films

SmCo(50 nm)/Fe(y nm) bilayers (y=0, 2.5, 5, 20) were prepared by magnetron sputtering on Si substrates. The films showed coercivities in the range 1.5–14 kOe as well as remanence enhancement, characteristic of exchange-coupled systems. Henkel plots for these bilayers showed that the demagnetizing interactions increase as the thickness of the Fe layer increases. For each film, a set of minor loops was measured in order to determine the Preisach distributions. With suitable analytic forms for these distributions, we obtained a description of the experimental data for the major loops, the minor loops and recoil curves. The comparison with experiment is excellent. From the moving Preisach model we have determined the evolution of the reversible and irreversible magnetization components during the magnetization and demagnetization processes. The most important source of Mrev is the reversible rotation of the magnetization in the grains of the SmCo layer. The soft Fe layer, when well coupled to the SmCo layer, contributes mainly to Mrev, but is also an important source of Mirr.

Dependence of the anhysteretic magnetization on the demagnetization factor

A method is presented to measure the dependence of the anhysteretic magnetization curve (the anhysteretic magnetization as a function of the internal field after degaussing) on the demagnetization factor N without physically varying N. The relation between the Preisach distribution and the N dependence of the anhysteretic magnetization curve is discussed in a way that is very close to the work of Bertotti. Classes of (moving) Preisach models are identified for which the anhysteretic magnetization curve is independent of the demagnetization factor. It is proven that the anhysteretic magnetization increases with N at fixed internal field, if the Preisach distribution decreases monotonically with increasing H cent, the internal field value of a Preisach domain. It is shown that the Moving Preisach model may lead to a negative anhysteretic permeability.

Reversible and irreversible magnetization behavior in SmCo films

Recent studies of demagnetization processes in permanent magnets have used two different methods for determining the reversible magnetization, often arriving at conflicting results. In the present work, enhanced-remanence SmCo films have been prepared by DC magnetron sputtering. The evolution of the reversible ( M rev) and irreversible ( M irr) magnetization along the initial magnetization curve and the demagnetization curve of the films was determined using the two methods. In one case, the DCD definition of the reversible magnetization was used to measure the quantity from a set of recoil curves. Alternatively, the moving Preisach model was used to separate the magnetization into its components M rev and M irr. We discuss the different behaviors encountered for the reversible magnetization and the inter-relation function η=(∂ M rev/∂ M irr) Hi and interpret the differences.

Generalized δm curves for particulate recording media obtained by Fourier analysis

The generalized /spl delta/m/sub a/ curve obtained by the Fourier analysis of the first magnetization and major hysteresis loop is analyzed within the frame of a generalized moving Preisach model. Analytical expressions of the Fourier coefficients are obtained when the mean field interactions are negligible. Experimental and simulated /spl delta/m and /spl delta/m/sub a/ curves are obtained for commercial particulate recording tapes. The condition is established for using the generalized curves instead of the classical ones in particulate media.