Irreversible Magnetization Components Research Articles

Accurate calculation of global hysteresis properties of grain-oriented silicon steel based on an improved J-A model with variable parameters

Based on the consideration of the magnetic domain motion under different magnetization levels, an improved J-A model with variable parameters is proposed to solve the problem of significant errors in the process of calculating the inner symmetric small loops. The proposed method introduces a variable scale parameter v(B) to correct the irreversible magnetization component of the J-A model. Meanwhile, based on the magnetic domain theory, a method with variable pinning parameter k(B) and a variable domain wall bending parameter c(B) is proposed. By comparing the measured data of B30P105 Grain-Oriented (GO) silicon steel, the calculation error for each magnetization level of the model is within 7%, which means that the global hysteresis properties of GO silicon steel can be well reproduced.

Magnetic properties of FeCo-iron oxide core–shell nanoparticles investigated through first order reversal studies

Core–shell magnetic nanoparticles exhibit exchange bias, whereas the magnitude of the exchange bias field is influenced by various factors that are still under investigation. We present a detailed analysis of the magnetic behavior in Fe- and Co-rich FeCo particles with a ferrimagnetic oxide shell. The as-synthesized alloys, with an average particle size above 150 nm, show high saturation magnetization and exhibit multidomain nature. The magnetic behavior has been analyzed through first order reversal studies at room temperature, and low temperature (15 K) for the as-synthesized and size-reduced alloys. The size-reduced alloys exhibit exchange bias that enhances with decreasing average particle size and found to be maximum for the Co-rich FeCo. First order reversal curve (FORC) studies could resolve the reversible, irreversible magnetization components, and magnetostatic interactions. The low-temperature field cooled measurements expose random field bias acting at the interfaces. The studies reveal that FORC could be utilized to obtain information about particle size and its distribution dependent magnetic behavior in core–shell nanostructures.

Probing the interplay between reversibility and magnetostatic interactions within arrays of multisegmented nanowires

Ordered arrays of NiFe/Cu multisegmented nanowires (NWs) are fabricated by ac pulse electrodeposition method into the 25-µm thick anodic aluminum oxide templates with a pore diameter of about 40–100 nm inter-pore distance. The behavior of magnetostatic interactions between neighboring NiFe/Cu NWs as well between magnetic segments of the same wire related to the NW length and the magnetic segment thickness is presented. The first-order reversal curves (FORCs) results for two given magnetic shape anisotropies, a nearly disk-shaped and a rod-shaped one, reveal a single domain magnetic state along with a constant peak value of FORC coercivity distribution (H FORC ). However, the Major Hysteresis Loop coercivity (H MHL ) shows a significant reduction with an increase in length. In addition, the magnetostatic interaction distribution along the Hu axis of FORC diagrams shows a weakly decreasing behavior, in disagreement with existing phenomenological model. In order to resolve this contradiction, the reversible and irreversible components of magnetization were measured. For arrays of multisegmented NWs, the contribution of the reversible components of magnetization rises up to about 70% as NW’s length increases which is in contrast for arrays of uniform NWs where a nearly zero reversibility is reported.

Magnetic reversal and magnetic memory effect in melt-spun Pr2Fe14B/α-Fe nanocomposite ribbons

The influence of CoCr addition on the microstructure and magnetic properties was investigated in nanocomposite Pr2Fe14B/α-Fe alloys prepared by melt spinning. It was shown that the magnetic properties of Pr2Fe14B/α-Fe nanocomposite were improved by an addition of 10 at.% CoCr, in particular, coercivity (jHc) from 4.9 up to 5.3 kOe, maximum energy product ((BH)max) from 10.6 up to 13.9 MGOe, and remanence (Mr) from 94.2 up to 98.4 emu/g. The field dependencies of the reversible and irreversible magnetization components were derived from the recoil loops. Combining with the initial magnetization curves, the results indicated that the pinning of domain walls at the grain boundaries dominated the magnetization reversal in Pr2Fe14B/α-Fe nanocomposite alloys. The magnetic memory effect was studied by measuring the magnetic moment relaxation at a cycle negative magnetic field with time interval of 600 s. The exchange-spring magnets with magnetic memory effect have a high potential for high density magnetic recording.

The Magnetization Reversal Processes Of Bulk (Nd, Y)-(Fe, Co)-B Alloy In The As-Quenched State

Abstract The magnetization reversal processes of bulk Fe64Co5Nd6Y6B19 alloy in the as-quenched state have been investigated. From the analysis of the initial magnetization curve and differential susceptibility versus an internal magnetic field it was deduced, that the main mechanism of magnetization reversal process is the pinning of domain walls at the grain’s boundaries of the Nd2Fe14B phase. Basing on the dependence of the reversible magnetization component as a function of magnetic field it was found that reversible rotation of a magnetic moment vector and motion of domain walls in multi-domain grains result in high initial values of the reversible component. The presence of at least two maxima on differential susceptibility of irreversible magnetization component in function of magnetic field imply existence of few pinning sites of domain walls in Fe64Co5Nd6Y6B19 alloy. The dominant interactions between particles have been determined on the basis of the Wohlfarth dependence. Such a behavior of Wohlfarth’s plot implies that the dominant interaction between grains becomes short range exchange interactions.

Tuning magnetic fingerprints of FeNi nanowire arrays by varying length and diameter

Magnetic nanowires (NWs) electrodeposited into solid templates are of high interest due to their tunable properties which are required for magnetic recording media and spintronic devices. Here, highly ordered arrays of FeNi NWs with varied lengths (ranging from 2.5 to 12 μm) and diameters (between 45 and 75 nm) were fabricated into anodic aluminum oxide templates using a pulsed ac electrodeposition technique. X-ray diffraction patterns along with energy dispersive spectroscopy indicated the formation of Fe70Ni30 NWs with fcc and bcc alloy phases, being highly textured along the bcc [110] direction. Magnetic properties were studied by hysteresis loop measurements at room temperature and they showed reductions in coercivity and squareness values by increasing length and diameter. Further, magnetic fingerprints of the NWs were characterized using the first-order reversal curve (FORC) analysis. FORC measurements revealed that, with increasing length and diameter from 2.5 to 10 μm and 45–55 nm, respectively, besides an increase in inter-wire magnetostatic interactions, a transition from a single domain (SD) state to a pseudo SD state occurred. Moreover, a multi-domain (MD) state was found for the longest length and diameter. While the irreversible magnetization component of the SD NWs was approximately 100%, the reversible component of MD NWs increased up to 20%.

Magnetization reversal processes in bonded magnets made from a mixture of Nd–(Fe,Co)–B and strontium ferrite powders

Isotropic epoxy-resin bonded magnets composed of different amounts of Magnequench MQP-B and strontium ferrite powders have been prepared using a compression molding technique. The magnetic parameters for magnets with different amounts of strontium ferrite and magnetization reversal processes have been studied by the measurement of the initial magnetization curves, the major hysteresis loops measured at a field up to 14T and sets of recoil loops. The enhancement of μ0MR and μ0HC is observed in comparison with the calculated values. From the recoil loops the field dependences of the reversible, irreversible and total magnetization components and the differential susceptibilities were derived. From the dependence of the irreversible magnetization component versus an applied field it was deduced that the main mechanism of magnetization reversal process is the pinning of domain walls in MQP-B and strontium ferrite grains. The interactions between the magnetic particles and grains have been examined by the analysis of the δM plot. The δM behavior of magnets with ferrite has been interpreted as being composed of magnetizing exchange coupling and demagnetizing dipolar interactions.

Study of the magnetic interaction in nanocrystalline Pr–Fe–Co–Nb–B permanent magnets

The magnetic properties of an isotropic, epoxy resin bonded magnets made from Pr–Fe–Co–Nb–B powder were investigated. The magnetization reversal process and magnetic parameters were examined by measurements of the initial magnetization curve, major and minor hysteresis loops and sets of recoil curves. From the initial magnetization curve and the field dependencies of the reversible and irreversible magnetization components derived from the recoil loops it was found that the magnetization reversal process is the combination of the nucleation of reversed domains and pinning of domain walls at the grain boundaries and the reversible rotation of magnetization vector in single domain grains. The interactions between grains were studied by means of δM plots. The nonlinear behavior of δM curve approve that the short range intergrain exchange coupling interactions are dominant in a field up to the sample coercivity.The interaction domains and fine magnetic structure were revealed as the evidence of exchange coupling between soft α-Fe and hard magnetic Nd2Fe14B grains.

The magnetization reversal processes of Sm 2Gd 10.5Fe 8Co 64Zr 2.5Cu 13 alloy in the as-quenched state

The magnetization reversal processes of the as-quenched Sm 2Gd 10.5Fe 8Co 64Zr 2.5Cu 13 ribbons obtained by melt-spinning method have been investigated. From the analysis of the initial magnetization curve it was deduced that the main mechanism of magnetization reversal process is the pinning of domain walls at the grain's boundaries. From the dependence of the reversible magnetization components as a function of magnetic field it was found that reversible rotation of magnetic moment vector results in high initial values of this component. The presence of several maxima on the differential susceptibility curves derived from the irreversible magnetization component in both direction of magnetization implies existence of several pinning sites for domain walls. The interaction between the alloy grains have been examined by using the so-called δm( μ 0 H i) plot. The values of δm( μ 0 H) for investigated alloy remains positive for an applied field up to 1.15 T and negative for higher fields. Such behavior of δm( μ 0 H i) dependence certifies that the dominant interaction between grains is the short range exchange interactions but low values of δm( μ 0 H) implies that these interactions are week.

Accurate minor loops calculation with a modified Jiles‐Atherton hysteresis model

PurposeAlthough the original Jiles‐Atherton (J‐A) hysteresis model is able to represent a wide range of major hysteresis loops, in particular those of soft magnetic materials, it can produces non‐physical minor loops with its classical equations. The purpose of this paper is to show a modification in the J‐A hysteresis model in order to improve the minor and inner loops representation. The proposed technique allows the J‐A model representing non‐centred minor loops with accuracy as well as improving the symmetric inner loops representation.Design/methodology/approachOnly the irreversible magnetization component is slightly modified keeping unchanged the other model equations and the model simplicity. The high‐variation rate of the irreversible magnetization, which causes the non‐physical behaviour of minor loops, is limited by introducing a new physical parameter linked to the losses. Contrarily to other modifications of the original model found in the literature, the previously knowledge of the magnetic field waveform is not needed in this case.FindingsThe modified hysteresis model is validated by comparison with experimental results. A good agreement is observed between calculations and measurements. The modified model retains the low‐computational effort and numerical simplicity of the original one.Originality/valueThis paper shows that a classical scalar hysteresis model can be suitably used to take into account the minor loops behaviour and be included in a finite element code. The methodology is useful for the design and analysis of electromagnetic devices under distorted flux patterns.

Magnetization reversal mechanisms in hybrid resin-bonded Nd–Fe–B magnets

The magnetic properties of isotropic epoxy resin-bonded magnets prepared by mixing a hard magnetic powder made from melt quenched Nd–Fe–Co–B ribbons and a soft magnetic iron powder have been examined. The magnetization reversal processes and the magnetic parameters have been studied by the measurement of the virgin magnetization curves, the major and minor hysteresis loops and sets of recoil curves. From these recoil curves the field dependence of the reversible and irreversible magnetization components during the magnetization and demagnetization processes has been derived. The remanence relationship was used to study the nature of magnetic interaction between the grains. A study of interaction domains was conducted using optical microscopy. Groups of domains, each over several grains, were observed. It was found that the reversal process in the samples investigated involves the rotation of magnetization vectors in the iron powder grains and pinning of domain walls at the MQP-B grain boundaries.

Magnetic properties of anisotropic Nd–Fe–B resin bonded magnets

The magnetic properties of an anisotropic, epoxy resin bonded magnet made from Magnequench powder of MQA-T type were investigated. The magnetization reversal processes and the magnetic parameters were examined by measurement of virgin magnetization curve, the major and sets of minor hysteresis loops. The coercivity as a function of maximum magnetizing field were determined. The field dependence of the reversible and irreversible magnetization components during the magnetization and demagnetization processes was investigated by measuring sets of recoil curves. As it results from the initial magnetization curve shape and the field dependence of coercivity the magnetization reversal mechanism appeared to be the pinning one.

Inter-relation between reversible and irreversible magnetization components in nanocrystalline SmCo films

A study of the experimental behavior of the reversible ( M rev) and the irreversible ( M irr) DCD magnetization components in enhanced-remanence SmCo films was carried out. The evolution of the DCD M rev and M irr components were determined at room temperature by measuring sets of first-order reversal curves from different points on the initial magnetization curve and the demagnetization curve. From these data, M rev( M irr) H i curves were built, H i being the internal field of the sample. Recent studies show that the behavior of the M rev( M irr) curves at a constant internal field can be used as an indicator of the mechanism of reversal magnetization. The non-monotonic behavior showed by these curves at low fields in our material, seems to be associated with an incoherent mechanism of magnetization reversal in the nanograins of SmCo.

Modeling of interaction effects in granular systems

Interaction effects on the magnetic behavior of granular solid systems are examined using a numerical model which is capable of predicting the field, temperature and time dependence of magnetization. In this work, interaction effects on the temperature dependence of time viscosity coefficient S( T) and formation of minor hysteresis loops have been studied. The results for the time- and temperature dependence of remanence ratio have showed that the distribution of energy barriers f(Δ E) obtained depend critically on the strength and nature of interactions. These interactions-based changes in f(Δ E) can easily give a temperature-independent behavior of S( T) when these changes give a 1/Δ E behavior to the distribution of energy barriers. Thus, conclusions about macroscopic quantum tunneling must be carefully drawn when the temperature dependence of S( T) is used to probe for MQT effects. For minor hysteresis effects, the result shows that for the non-interacting case, no minor hysteresis loops occur and the loops are only predicted when the interaction field is positive. From these predictions, minor loops will form when the interaction field is strong enough to magnetize some moments during the recoil process back to zero field. Thus, these minor loops are originated from interaction driving irreversible changes along the recoil curve and the irreversible component of magnetization has no direct influence on the formation of these minor loops.

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.

Application of the Preisach model to nanocrystalline magnets

Experimental results are presented for several exchange-coupled nanocrystalline alloys of composition Sm 18(Fe,Co) 82 with different Fe contents. Minor loops, Henkel plots, and recoil curves are shown to be in excellent agreement with calculations performed using the moving Preisach model (MPM). Experimental reversible and irreversible magnetization components are found to be in excellent agreement with MPM simulations.

The measurement of irreversible magnetization and activation volumes

The phenomenological model of magnetization kinetics developed by Estrin et al. [J. Phys. 1, 4845 (1989)] yields a macroscopic magnetic equation of state or magnetic constitutive equation of functional form μ0H=f(Jirr,J̇irr), where, μ0H is the internal magnetic field, Jirr is the irreversible magnetic polarization and J̇irr its time derivative. In differential form the relation takes the form μ0 dH=(1/χirr)dJirr+Λd(ln J̇irr). The quantity Λ is related to the activation volume involved in the process of irreversible magnetization. To obtain Λ, three different experimental techniques are used. One involves the traversal of hysteresis loops at constant J̇irr, from which both χirr and Λ can be obtained most directly, using a modified version of a technique previously described. The second method involves traversing the hysteresis loop at constant μ0Ḣ, and subsequently separating the reversible and irreversible components of magnetization. In the third method, the parameter Λ is obtained from magnetic viscosity measurements, which is the technique most commonly used. Results are presented for all three experimental techniques for measurements performed on Alnico-type permanent magnets. The limitations of each method will be reviewed in relation to materials properties.

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. >

Nucleation fields in an exchange spring hard magnet

A detailed study of magnetization processes has been carried out on a new type of hard magnetic material. The material Nd3.8Fe73.3V3.9B18.0Si1.0 is unique among hard magnets due to the exchange coupling of two ferromagnetic materials, one of which is soft and the other hard. The combination of the two materials gives a composite material, with a high magnetic saturation and coercivity. The irreversible components of magnetization for the material were examined using the demagnetizing remanence curve (DCD) and the isothermal remanence curve (IRM) for the magnetizing case. The nature of the interactions in the material were also studied using the delta M plot obtained via the DCD and IRM remanence curves. The reversible components were obtained from the M-H loop data, Mrev=Mtot-Mirr. Measurements of magnetic time dependence have also been carried out to provide fluctuation field data, Hf, from which activation volumes of reversal, v, for various fields have been obtained. The mean activation field Ha, obtained by extrapolating the linear portion of the fluctuation field data to zero, is the same as the mean nucleation field Hn obtained from the reversible components, Mrev of the demagnetizing remanence curve. Assuming spherical volumes of reversal, the dimensions of the soft and hard phases, obtained from the mean volume of activation, v(Hn) are close to the critical dimensions of the soft and hard phases.

Mathematical modelling of hysteresis

This paper presents a formal mathematical treatment of the general properties of scalar hysteretic systems. A generalization of the Preisach representation including both irreversible and reversible components of magnetization is given. It is shown that the Mayergoyz’s theorem has a more general validity in this new representation. The effect of a linear feedback transformation on the existence of the generalized Preisach representation is considered, and the necessary and sufficient conditions for the invariance of such an existence are given. Finally the effect of the shape demagnetizing field on the relative weight of reversible and irreversible components of magnetization is discussed. The reversible component is found to be enhanced by the shape demagnetizing field. The results obtained in this paper are relevant not only for magnetic systems, but also for the mathematical modelling of any kind of hysteretic system.