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The Stoner–Wohlfarth model predicts the crossing of the ascending and descending branches of the hysteretic magnetization curve. This crossing behavior has widely been dismissed, with the claim that it violates the laws of thermodynamics. Experimental verification of hysteresis branch crossing has not been acknowledged in the literature. Here we show, both theoretically and experimentally, that the crossing of the ascending and descending branches of the magnetization curve is a robust, reproducible phenomenon which does not violate any fundamental law.

The modeling of hysteresis curves of bonded ferrite magnets is discussed. Hysteresis of anisotropic magnets were calculated according to the Stoner-Wohlfarth Model, for the cosn (theta) distribution. The crystallographic texture has significant effect on the hysteresis curve. Two different samples were examined, one isotropic and another anisotropic. The anisotropy field of strontium ferrite magnets was determined to be 19.5 kOe. The Mr/Ms ratio of the anisotropic bonded magnet was estimated as 0.8.

The purpose of this paper is to describe a finite-element method for the numerical simulation of magnetization and demagnetization processes in ferromagnetic pieces with hysteresis. In particular, the proposed methodology will be applied to compute the remanent flux density after a magnetic particle inspection test on specimens with cylindrical symmetry consisting of three stages: longitudinal magnetization, circular magnetization, and demagnetization.

This paper presents the extension of two 1-D lamination models with magnetic hysteresis to reproduce dynamic hysteresis loops and power loss in grain-oriented (GO) electrical steels. For this purpose, the concept of magnetic viscosity is introduced in the model equations. The applicability and accuracy are demonstrated by means of two GO steels of different thicknesses at magnetizing frequencies up to 1000 Hz. Advantages and limits of the classical approach with and without viscosity and comparisons to measured data are discussed in detail.

Anisotropy constants of magnetic materials are typically determined through angle-resolved Ferromagnetic Resonance (ar-FMR) and torque magnetometry, which can be time consuming measurements, thus limiting their utility. The Stoner–Wohlfarth model can be used to numerically fit measured magnetic hysteresis curves to more easily determine these anisotropy constants. To demonstrate this, 10 nm bct FexCoyMnz single-crystal films grown by molecular beam epitaxy on MgO(001) substrates were investigated. The hysteresis behavior measured by vibrating sample magnetometry was least-squares fit against numerically calculated hysteresis curves generated from the Stoner–Wohlfarth model to extract the anisotropy constants. The cubic anisotropy of different compositions of FeCoMn films was at ∼104 J/m3, which is on the same order of magnitude of bct Fe and Co thin films measured by ar-FMR and torque magnetometry techniques.

International audience; A series of strontium hexaferrites (Sr-HF) compounds, doped with a low amount of manganese SrFe12-xMnxO19 (where x = 0.00, 0.03 and 0.05), were prepared by a sol-gel method. Structural and microstructural characterizations were performed by X-ray diffraction (XRD) and scanning electronic microscopy (SEM) in order to determine some basic properties such as lattice parameters and particles size. Moreover, magnetic properties of the samples were measured in a temperature range from 2 to 900 K. The results show that the transition temperature (TC) decreases from 764 to 721 K with Mn doping at x = 0.05 content. Also, temperature and doping effects on the coercivity (Hc), the remanent magnetization (Mr) and the magnetization of saturation (MS) were discussed considering the Stoner - Wohlfarth model. A slight improvement of the magnetic properties (Hc =5.56 kOe, Mr =49.99 emu/g, MS =101.9 emu/g (i.e. 19.37 µB/u.f)) for low content (x = 0.03) is evidenced, yielding to promising material for permanent magnet devices. This improvement was explained by the relationship between the microstructure and to the effective magnetic anisotropy.

A formula has been derived for calculating the main magnetization curve of steels from the strength of the magnetizing field and the measurement results of the magnetization of technical saturation, coercive force, and residual magnetization. We analyzed the influence of material magnetic properties on the approximation of its magnetization to technical saturation.

Magnetization curves of an YFe3 single crystal were measured along the basal plane and the c-axis within the temperature range of 2–600 K. Their analysis provided temperature dependencies of the parameter p = ( M ep − M ha ) / M ep characterizing saturation magnetization anisotropy and magnetocrystalline anisotropy constants K1 and K2. The latter was obtained using the modified Sucksmith-Thompson method and the numeric technique of approximation which takes into account slight misorientation between applied magnetic field and the hard magnetization axis allowing to describe magnetization curves accurately.

Nickel substituted manganese ferrite [NixMn1−xFe2O4 (x = 0.2)] nanoplates with cubic shape and controlled sizes were fabricated by chemical coprecipitation technique. Structural analyses confirmed the formation of single phase crystalline nanoplates in the size range 8–24 nm. Magnetic studies showed that coercivity as a function of plate length goes through a maximum, peaking at 162 Oe and then decreases for larger nanoplates, indicating that the single domain limit for NixMn1−xFe2O4 (x = 0.2) is ∼21 nm. While negligible coercivity at below 10 nm confirms the superparamagnetic limit in the range 8–10 nm for these nanoplates. Saturation magnetization of the samples was found to increase linearly with plate length in the single domain regime, however this increase was observed slower for the larger nanoplates. Typical blocking effects were studied in the temperature range 20–300 K and it was found the superparamagnetic blocking temperature increases monotonically with increasing size of the nanoplates. The results are discussed in terms of the enhanced surface roles and variation of surface and effective anisotropies with size of the nanoplates that strongly influence their magnetic properties within the domain of Stoner Wohlfarth model for ferromagnetic systems.

The isotropic Stoner-Wohlfarth model can be applied for the determination of the anisotropy field in powders. Samples of strontium ferrite - SrFe12O19 – were measured in Vibrating Sample Magnetometer (VSM). By means of the fitting of the first quadrant of the hysteresis curve the anisotropy field was estimated as 19-20 kOe for the SrFe12O19 phase. The main advantage of the method is its simplicity, because compacting or sintering of the powder samples is not necessary

Arrays of nanosized hollow spheres of Ni were studied using micromagnetic simulation by the Object Oriented Micromagnetic Framework. Before all the results, we will present an analysis of the properties for an individual hollow sphere in order to separate the real effects due to the array. The results in this paper are divided into three parts in order to analyze the magnetic behaviors in the static and dynamic regimes. The first part presents calculations for the magnetic field applied parallel to the plane of the array; specifically, we present the magnetization for equilibrium configurations. The obtained magnetization curves show that decreasing the thickness of the shell decreases the coercive field and it is difficult to obtain magnetic saturation. The values of the coercive field obtained in our work are of the same order as reported in experimental studies in the literature. The magnetic response in our study is dominated by the shape effects and we obtained high values for the reduced remanence, $M_{r}/M_{S} = 0.8$ . In the second part of this paper, we have changed the orientation of the magnetic field and calculated hysteresis curves to study the angular dependence of the coercive field and remanence. In thin shells, we have observed how the moments are oriented tangentially to the spherical surface. For the inversion of the magnetic moments we have observed the formation of vortex and onion modes. In the third part of this paper, we present an analysis for the process of magnetization reversal in the dynamic regime. The analysis showed that inversion occurs in the nonhomogeneous configuration. We could see that self-demagnetizing effects are predominant in the magnetic properties of the array. We could also observe that there are two contributions: one due to the shell as an independent object and the other due to the effects of the array.

We have produced hot-deformed Nd-Fe-B magnets from commercial (MQU-F) Nd-Fe-B ribbons. The spark-plasma-sintering technique was used to deform the samples under low pressures of 40 MPa. The initial stages of the hot-deformation process were investigated in terms of microstructures and magnetic properties. Hot-deformed magnets with different deformation ratios were produced and the dependence of the remanence on the deformation ratio was determined. In the initial stages of the hot-deformation process, a cone-like shape of the magnet was observed for the first time. The experimental data can be qualitatively interpreted by applying the basic Stoner–Wohlfarth model.

In the fabrication of soft magnetic composite materials, the iron powder particles are submitted to a high-pressure compaction process that should be considered in the modeling of magnetic hysteresis. This paper introduces a novel approach for modeling the stress-dependent magnetic hysteresis, based on the Stoner–Wohlfarth (S–W) model. Moreover, for determining the S–W particle equilibrium orientation directly, an extended S–W astroid method, which considering the stress effect, is presented. To verify this presented model, the magnetic hysteresis phenomenon of SOMALOY 500 are measured and simulated. The comparison between the two results shows that this model is feasible and effective, which can be applied to practical engineering.

The Alnico magnets (also called Ticonal) have coercivity attributed to shape anisotropy. The conditions for appearing this type of anisotropy are discussed, and the principal is the existence of elongated grains parallel to the easy magnetization axis. A very important detail is that the conditions assumed in the Stoner Wohlfarth model have to be obeyed. The assumptions are i) ferromagnetic phase with single domain particle size and ii) grains without magnetic interaction between them, magnetically insulated by a grain boundary paramagnetic phase. In Alnico magnets, the coercivity mechanism is coherent rotation of single domain size particles.

The ratios of Fe/Co and Fe/B in a ferromagnetic alloy system, Fe(87-x-y) Co(x) Ti7 Zr6 By (x = 20, 30, and 40 at% and y = 2 and 4 at%), which was produced by the melt-spinning technique in the form of thin ribbons, were investigated to improve the saturation magnetization. The thermal properties T(x) were in the range of 792.0 K to 838.0 K, and it decreased by decreasing Fe/Co ratio. In the as-spun amorphous ribbons, the saturation magnetization and coercivity ranged from 137.5 emu/g to 164.2 emu/g and from 0.027 Oe to 1.245 Oe, respectively. The optimum Fe/Co ratio for the Fe(83-x) Co(x) Ti7 Zr6 B4 system was determined to be 64:36. In other words, the optimum system was Fe60 Co25 Ti7 Zr6 B2, which exhibited robust soft magnetic properties, such as a low coercivity of 0.252 Oe, and high saturation magnetization of 164.2 emu/g (1.55 T). Also, in this system, magnetic properties such as the saturation magnetization and coercivity increased with decreasing Fe/Co ratio.

A numerical extension of the simple Stoner–Wohlfarth model to the case of bi-dimensional angular distributions of easy axis is provided. The results are particularized in case of step-like, Gaussian-like and user defined distributions. In spite of its simplicity, the model can be applied to magnetically textured thin films and multilayers with in-plane magnetic anisotropy, independently on the texture source. Exemplifications are provided for a simple ferromagnetic textured FeCo film as well as for a FeMn/FeCo/Cu/FeCo spin valve structure.

The Nd9.5Fe61.5Co10Nb20.5Ti0.5B15.5C0.5 nanocomposite magnets have been prepared by the copper-mold casting technique. The magnetic properties were calculated by the micromagnetic simulation using the magnetic force microscopy image. The influence of different saturation magnetization of amorphous grain boundary phase on the magnetization reversal process was investigated. The simulation results indicate that the coercivity increases with the reducing saturation magnetization of amorphous phase when the grain size varied from 300 to 1000 nm. The magnetization reversal process demonstrates that the magnetic moments of NdFeB phase show the prior inversion at the grain boundaries. Furthermore, the comparison between the anisotropic and isotropic model implies the importance of preparing anisotropic magnets.

The remanence and coercivity of arc melted Mn70Ga30 can be substantially improved by cold rolling. For best performance the rolled material should be annealed at T=730 K in the presence of a magnetic field of 1 T. The so-obtained magnet has a remanence of 0.239 T and a coercivity of 1.24 T at room temperature. The underlying reason for the high coercivity and remanence is the increase of the content of a metastable ferrimagnetic D022 phase at the expense of the normally stable anti-ferromagnetic D019. Magnetic field significantly increases the nucleation rate of the ferromagnetic D022 phase that leads to grain size refinement and as a consequence of improving remanence and coercive field.

Room-temperature magnetic properties of planar nanowire arrays of Fe have been studied using comprehensive analysis of FMR and magnetometry data. It has been shown that the Fe NWs are ferromagnetic at room temperature and their magnetic properties are mainly governed by shape anisotropy. Combining parameters derived from the FMR study with experimental data of magnetometry, simulations of hysteresis loops have been performed based on Stoner–Wohlfarth approach. Calculations show that magnetisation reversal of Fe NWs has a coherent-rotation type of localised character. As NW thickness decreases, localisation of the magnetisation reversal mode is found to enhance due to increased inhomogeneity of thinner NWs.

This paper presents a vector hysteresis model based on micromagnetic theory. In this model, a magnetization state of a magnetic material is described by a collection of single-domain particles, and magnetic reversal processes due to domain-wall motions are treated approximately as a magnetization flip. The present model is applied to calculation of hysteresis properties of grain-oriented silicon steel. The simulation results show that the anisotropic hysteresis properties and iron loss can be reproduced accurately by the present model.

The remanence of a ferromagnet is formed under the influence of many factors, the main of which are a magnetic field (DC and AC), temperature, mechanical stress, and chemical transformations. Remanences obtained by different ways are differently resistant to external influences. Remanence observed in structural elements may result from one factor or from all of the above. It is shown that the use of remanence as a parameter for assessing the stress-strain state, i. e. the “method of magnetic memory”, without taking into account the conditions of the formation of the remanence state in a product area under testing will have low assessment reliability.

The magnetic properties of Lycopodium powders from two different sources are investigated. In addition to a characteristic diamagnetism with χ = -8(1) × 10 -6 , there is a Curie-law paramagnetism, which is the dominant contribution to the susceptibility below 20 K, and an additional weak hysteretic signal with a saturation magnetization of magnitude 0.6-1.8 × 10 -3 Am 2 kg -1 at room temperature. After ignition of the powder, the remaining inorganic ash represents just 1.05% of the original mass, but the room temperature magnetization increases only by a factor of 5. The iron content of the Lycopodium, deduced by chemical analysis of the ash is 43-76 ppm. Of this, roughly 3/4 is paramagnetic, and 1/4 is in the form of magnetite.

Die upsetting is an effective method to produce bulk anisotropic Nd-Fe-B magnets with nanostructure and full density [1]. A variety of experimental evidence suggests that the grain boundary a play key role in magnetic hardening [2]. Therefore, the grain boundary diffusion method is an effective way to improve the coercivity of die-upset magnet [3, 4]. However, the special role of the grain boundary after diffusion on both magnetic structure and microstructure of the die upsetting magnets is unclear and controversial. In order to obtain the excellent coercivity in the die-upset nanocrystal-line magnets, it is necessary to get better understanding on the mechanism of the enhanced coercivity. In this work, we have fabricated nanocrystalline Nd-Fe-B magnets by hot pressing and die upsetting methods with low melting point eutectic Nd-Cu alloy addition. The coercivity has been dramatically enhanced by Nd-Cu alloy addition. To investigate mechanism of the enhancement of the coercivity, we observed microstructure and the initial magnetization curve of the die upsetting magnets with different Nd-Cu addition.

Magnetic nanostructures with perpendicular magnetic anisotropy (PMA), as compared with the spin valves with in-plane anisotropy, have a lower level of thermal magnetization noise due to the high value of PMA, as well as a lower critical current density required for magnetization reversal nanostructures [1, 2].

© 2016 IEEE. This paper proposes a vectorial magnetic hysteresis model based on a vectorial elemental operator and its distribution function to represent the magnetization mechanisms of soft magnetic materials. The magnetic hysteresis of a soft magnetic composite material under rotational magnetization is simulated and compared with the experimental results.

© 1982-2012 IEEE. Magnetorheological fluid (MRF) materials are used in many devices as smart materials. However, the application of this material is limited to damper or vibration absorber because of the lack of understanding of its magnetic hysteresis properties. This paper systematically presents our recent investigation and simulation on the magnetic hysteresis properties of MRF materials. The measurement of its magnetic hysteresis property was accomplished by using a two-dimensional single sheet tester with an MRF sample container. An extended large-scale atomic/molecular massive parallel simulator, which is combined with the Stoner-Wohlfarth hysteresis model, was employed for simulating the magnetic hysteresis properties of MRF material. The measurement and simulation results are compared, analyzed, and discussed. The results will be useful for modeling of magnetic hysteresis properties of MRF materials.

A new hysteresis operator for the simulation of Goss-textured ferromagnets is here defined. The operator is derived from the classic Stoner–Wohlfarth model, where the anisotropy energy is assumed to be cubic instead of uniaxial, in order to reproduce the magnetic behavior of Goss textured ferromagnetic materials, such as grain-oriented Fe–Si alloys, Ni–Fe alloys, and Ni–Co alloys. A vector hysteresis model based on a single hysteresis operator is then implemented and used for the prediction of the rotational magnetizations that have been measured in a sample of grain-oriented electrical steel. This is especially promising for FEM based calculations, where the magnetization state in each point must be recalculated at each time step. Finally, the computed loops, as well as the magnetic losses, are compared to the measured data.

The barium and strontium hexaferrites (BaM and SrM) were successfully prepared by the standard solid-state reaction method. To inhibit crystal growth, 1 wt % B2O3 was added into the initial mixture. The structural and magnetic properties of pure hexaferrites were compared with the samples prepared with boron addition. Powders were annealed at temperatures between 800 and 1200 degrees C. The crystal structure, morphology, and magnetic properties of hexaferrites were investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). BaM was synthesized at temperatures as low as 800 degrees C with boron addition having saturation magnetization of similar to 50 emu/g and coercivity of similar to 3 kOe. At the same temperature, pure sample has very low magnetization about 1.3 emu/g. Moreover, at higher sintering temperatures, boron-containing samples have higher magnetization values compared to pure BaM. The optimal Fe/Ba ratio was determined as 10.5 for boron-containing samples, while it is 11.5 for the pure one. The coercivity started to decrease at 1100 degrees C indicating that single to multi-domain transition occurs. The saturation magnetization values are nearly equal in pure- and boron-containing SrM samples in the whole temperature range. However, maximal coercivities occurred at different temperatures for boron-containing and the pure samples as 1000 and 1100 C-degrees, respectively. Magnetic interactions deduced from the Stoner-Wohlfarth model using the isothermal magnetization and demagnetization measurements showed that boron addition suppresses the destructive (demagnetizing-like) interactions among domains in both SrM and BaM samples, and thus, stabilizes the remanence.

Soft magnetic composite (SMC) material produced by powder metallurgical techniques is assumed to be an isotropic material. It is applied in the core with special structure of rotating electrical machines, in which, the local magnetic flux density varies with time depend on both magnitude and orientation. Magnetic anisotropic feature may be shown in the material and influences the core operational performance. By using the designed 3-D magnetic properties tester, this paper presents the alternating and rotational magnetic properties of the SMC materials. Slightly anisotropic properties are found in hysteresis features and core loss distributions along different magnetization directions or planes. Experimental results show that some direction of the testing specimen seems harder to be magnetized than other directions. Milling and pressing process of the bulk specimen may cause changing of the grain size, micro-strain and pinning. These can influence the coercivity and remanence of the material and cause magnetic anisotropy, which may also be enhanced by increasing frequency and magnetization.

The paper presents the results of theoretical and experimental research of the the effect of perturbation of the magnetization of a magnetic fluid caused by thermal fluctuations in an adiabatic sound wave in the initial area of the magnetization curve. Measurements are conducted on samples of a magnetic colloid with various viscosity of the dispersion medium in the frequency range of 20–60 kHz. In this frequency range, the studied samples are characterized by the absence of thermal relaxation of magnetization. Comparison of the conclusions of the thermal magnetization relaxation model with the results of experiment make it possible to obtain information on the rheological features of the neareast molecular environment of a particle, i.e., nanorheology.

The magnetic properties of nanocrystalline cobalt ferrite could be tuned with substituting small amount of non-magnetic rare earth cation at Fe site in cobalt ferrite. The variation in magnetic parameter of samples could also be obtained by measuring its anhysteretic magnetization curve without tailoring its chemical composition. The magnetic parameters such as coercivity, remanent magnetization and saturation magnetization critically depend upon different values of external magnetic fields. In the present study, the anhysteretic magnetization curve of the samples CoFe2−xLaxO4 (x=0.025, 0.05, 0.075 and 0.1) has been recorded and response of coercivity to different maximum values of applied field has been investigated. It has been observed that the response of coercivity to different maximum values of applied field shows non-linear behavior. The analysis of the response of coercivity to different values of applied field in low field regime has been carried out with the help of Rayleigh laws. The analysis of the plot yields significant information about magnetic anisotropy.

Fe-Ni graded films have been prepared by co-sputtering permalloy and Fe targets at different time-power sequences. Morpho-structural and magnetic investigations have been performed by transmission electron microscopy, Xray reflectometry, conversion electron Mossbauer spectroscopy and magneto-optic Kerr effect vector magnetometry, proving the thickness dependence of the properties. A magnetization reversal involving the displacement of Bloch-type walls is characteristic for a 115 nm thick Fe-Ni graded film whereas an in-plane coherent rotation of the spins, according to a Stoner-Wohlfarth mechanism was evidence for a 23 nm thick Fe-Ni graded film.

In this paper, we discuss the numerical modeling of hysteresis in magnetic steels with oriented and nonoriented grain. The modeling is fully 3-D, but it is applied here to typical 2-D magnetic problems. Starting from a vector generalization of the Preisach model, we introduce here the concept of an operative magnetic field, function of the state of magnetization of the material. This operative field is introduced to reproduce with more accuracy the peculiar behavior of Si-Fe steels approaching the saturation state. The properties of the model are discussed and some examples are reported.

We report magnetic properties of transition metal (TM) doped ZnO nanoparticles and compare the doping effects of different transition metal ions into the ZnO matrix. Stoner–Wohlfarth model has been used to study the switching behavior of magnetic moments by observing energy diagram and hysteresis. Low magnetic anisotropy in Zn1-xMxO nanoparticles is observed where M=Fe, Co, Ni and x is the dopant amount. We have considered chemical precipitation technique for the preparation of Zn1-xMxO samples and have compared the reversal processes of magnetic moments with respect to time in the nanoparticles.

The Stoner-Wohlfarth model can be used for predicting hysteresis curves of either isotropic or anisotropic nanocrystalline Sm2Co17 type magnets. For isotropic magnets, with Mr/Ms=0.5, the Stoner-Wohlfarth model predicts coercive force of 48% of the anisotropy field. Here, Mr is remanence and Ms is magnetization of saturation. Two texture distributions were compared: Pearson VII and cosn. The calculations indicate that increasing the alignment degree of the grains, the coercivity increases. However, this increase of the coercive force is small. It is found that a very well aligned magnet, with Mr/Ms ratio of 0.96, presents coercivity only ~20% higher than that of the isotropic magnet.

The special hysteresis characteristics of a laminated core (LC) under AC-DC Hybrid magnetization are obtained by test. The field-circuit coupled time-periodic finite-element method (TPFEM) combined with the fixed-point method is used to calculate the exciting current and magnetic field of the LC based on the DC-biased magnetizing curve. The behavior of LC with no-load and different loads under AC-DC Hybrid magnetization is analyzed based on the TPFEM.

Ni nanorods are dispersed into gelatine gels and used as nanoprobes to estimate the shear modulus of the surrounding gel matrix by magnetization measurements. The nanorods are synthesized via pulsed electrodeposition of Ni into porous alumina, released from the templates by dissolution of the oxide layer and after several processing steps dispersed into gelatine gels with an isotropic orientation-distribution. Magnetization measurements of the resulting gels show a significant influence of the gelatine concentration on their magnetic behavior. In particular, with decreasing gelatine concentration the measured coercivity is reduced indicating a mechanical rotation of the nanorods in the field direction. A theoretical model which relates the measured coercivity to the shear modulus of the surrounding gel matrix is introduced and applied to investigate the ageing process of gelatine gels with different gelatine concentrations at room temperature.

We have analyzed the magnetization curves measures by using VSM and MOKE in synthetic antiferromagnetic coupled CoB/Ru/CoB thin film. The measured results were compared with calculated ones by Stoner-Wohlfarth model based on the magnetization behavior of two ferromagnetic layers (, ). The calculated total magnetization ($M_{tot}

The magnetic hysteresis loop is a significant performance of ferromagnetic material. The different-size specimens were fabricated and studied on the basis of magnetomechanical coupling tests. The curve of relationship between model size and magnetization intensity is obtained and hysteretic curve is described in the different conditions. The results indicate that the influencing law is reflected based on size effect of model specimens and performance of magnetic hysteresis and magnetization intensity. The results indicate that the size of Q235 steel model specimens is considerably influential in the magnetic hysteresis loop and magnetization, which accounts for an evident size effect.

Ferrimagnetic nanoparticles of CoFe2O4 about 4–16 nm in diameter were synthesized by pyrolysis of a mixture of Fe and Co acetylacetonates. The field dependences of magnetization and hysteresis loops were investigated in magnetic fields up to 4000 kA/m at various temperatures from 4.2 to 500 K. A considerable contribution, positive or negative depending on the temperature, of “surface” anisotropy to the effective magnetic anisotropy of the nanoparticles was observed. A correlation was found between the magnetic properties that represent the specificity of small particles, namely, between “surface” anisotropy, magnetization, and high-field susceptibility.

The microstructure and magnetic properties of 2:17 type isotropic magnets were investigated. The slow cooling heat treatment (cooling at 1 °C/min from 820 to 400 °C, and isothermal treatment during 24 h) was interrupted after the temperatures of 820, 700, 600 and 500 °C and their hysteresis were measured with fields up to 9 T. The fully heat treated sample presented coercivity (μ0H) of 3.32 T, after 24 h at 400 °C. The microstructure was investigated with SEM–FEG (Scanning Electron Microscope with Field Emission Gun) and X-ray Diffraction Rietveld analysis. The application of the Stoner–Wohlfarth–Callen–Liu–Cullen (SW–CLC) model points out exchange coupling between ferromagnetic Sm2(CoFe)17 nanocells and ferromagnetic Sm(CoCu)5 present at the cell boundary phase. The results are interpreted with the double shell model: first-a cobalt-rich ferromagnetic Sm(CoCu)5 shell originates exchange coupling and second-a copper-rich paramagnetic Sm(CuCo)5 shell produces magnetic decoupling. This double shell helps to maximize coercivity and remanence. The anisotropy field of the Sm2(CoFe)17 cell phase was estimated in 7 T with the SW–CLC model.

Isolated magnetic nanowires have been studied extensively and the magnetization reversal mechanism is well understood in these systems. But when these nanowires are joined together in different architectures, they behave differently and can give novel properties. Using this approach, one can engineer the network architectures to get artificial anisotropy. Here, we report six-fold anisotropy by joining the magnetic nanowires into hexagonal network. For this study, we also benchmark the widely used micromagnetic packages: OOMMF, Nmag, and LLG-simulator. Further, we propose a local hysteresis method by post processing the spatial magnetization information. With this approach we obtained the hysteresis of nanowires to understand the six-fold anisotropy and the reversal mechanism within the hexagonal networks.

International audience; Some soft magnetic materials are strongly dependent of the temperature, because of their low Curie temperature. In order to predict their behavior in electrical devices, engineers need hysteresis models able to take into account the temperature. This paper is an attempt to take into account the temperature in an existing model of static hysteresis through its parameters. Variations of some parameters with temperature are issued or build thanks to the literature. At the end, all needed parameters have an analytical law versus temperature. Simulation results are compared to measurements and discussed.

The calculation of hysteresis curves with the Stoner-Wohlfarth model is somewhat laborious. For the Nd2Fe14B phase, the second order magnetocrystalline anisotropy (K2) constant is relevant, and this case only has been discussed in some studies. In this article, a simple algorithm for the calculation of the Stoner-Wohlfarth model for isotropic NdFeB magnets is described. This algorithm makes easier the modeling of the hysteresis curves of bonded melt-spun NdFeB magnets.

The magnetic response of nanocomposites formed by non-interacting well dispersed γ-Fe 2 O 3 nanoparticles in a polymer matrix is presented. Various low loading fraction of particles in polymer leads to an observation of similar values of blocking temperatures and coercive fields. ac response confirms that particles are non-interacting and follow Neel–Brown model. Effect of particle size distribution on hysteresis behavior and saturation magnetization as a function of temperature is discussed. Since particles have a size distribution, the experimental results of magnetic response are compared with simulations based on Stoner–Wohlfarth model of single size particles. We have devised a measurement method in which a constant magnetic field was applied while the thermal energy is varied by sequentially heating and cooling the sample below the blocking temperature. Nanoparticle–polymer composites show reversible magnetization behavior for sequential heating/cooling cycles. However, simulation based on single size particle system shows irreversible magnetization behavior during the heating and cooling cycles. These observations are qualitatively explained in terms of different behavior of magnetization as a function of temperature for smaller superparamagnetic particles and larger blocked particles below overall blocking temperature of the composite.