The correlations between processing parameters and magnetic properties of an iron–resin soft magnetic composite

In this study, internal microstrain of an iron–resin composite produced by powder metallurgy has been calculated using the Williamson–Hall method. The effects of microstrain evolution during different processing conditions on magnetic properties such as coercive force and hysteresis loss have been investigated. The results show that there are regular and similar changes of coercivity and hysteresis loss. Both of these properties are directly dependant on the pinning effect of the internal microstrain against the movement of magnetic domain walls during magnetization process.     

Magnetic properties of soft magnetic composites prepared with crystalline and amorphous powders

Physical properties of soft magnetic composites prepared with a mixture of amorphous (FeSiBC) and crystalline (Fe) powders coated with distinct electrical insulator contents are reported. Density, saturation polarization, permeability and coercivity of the cores reduce linearly with the increase of the softer magnetic phase amount and a general relation can be expressed by a rule of mixtures. The behavior of the coercivity, as a function of the magnetic phase content, differs from that previously reported for magnetic composites prepared with equal amounts of magnetic and non-magnetic phases. For frequencies upto 1 kHz the magnetic losses of the cores are constant, following the same behavior of the coercivity. A qualitative explanation of the behavior of the latter is addressed based on an expression applicable for crystalline and amorphous materials.     

Effect of warm compaction on the magnetic and electrical properties of Fe-based soft magnetic composites

This paper investigates the effect of warm compaction on the magnetic and electrical properties of Fe-based soft magnetic composites at operating frequencies between 0.1 and 10 kHz. The magnetic and electrical properties of samples were measured by an LCR meter and morphology of the samples was characterized by scanning electron microscopy. It was shown that the compacted sample prepared at 800 MPa and 550 °C had the lowest magnetic loss and electrical resistivity, and highest magnetic induction and effective permeability in comparison with other samples compacted at 800 MPa and room temperature, 150, 250, 350 and 450 °C.     

Magnetic properties of iron-based soft magnetic composites with MgO coating obtained by sol-gel method

Soft magnetic composites with a thin MgO insulating layer were produced by a sol-gel method. Energy dispersive X-ray spectroscopy, X-ray analysis, Fourier transform infrared spectroscopy, density measurement and compositional maps confirmed that thin layers of MgO covered the iron powders. Coercivity measurement showed that the stress relaxation and reduction of hysteresis loss efficiently occurred at 600 °C. At this temperature, the phosphate insulation of commercial SOMALOY^TM samples degrade and their electrical resistivity, magnetic permeability and operating frequency decreases noticeably. The results show that the MgO insulation has a greater heat resistance than conventional phosphate insulation, which enables stress-relief at higher temperatures (600 °C) without a large increase in eddy current loss. The results of annealing at 600 °C show that the electrical resistivity and ferromagnetic resonance frequency increased from 11 μΩ m and 1 kHz for SOMALOY^TM samples to 145 μΩ m and 100 kHz for the MgO insulated composites produced in this work.     

Annealing effects on magnetic properties of silicone-coated iron-based soft magnetic composites

This paper focuses on novel iron-based soft magnetic composites synthesis utilizing high thermal stability silicone resin to coat iron powder. The effect of an annealing treatment on the magnetic properties of synthesized magnets was investigated. The coated silicone insulating layer was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. Silicone uniformly coated the powder surface, resulting in a reduction of the imaginary part of the permeability, thereby increasing the electrical resistivity and the operating frequency of the synthesized magnets. The annealing treatment increased the initial permeability, the maximum permeability, and the magnetic induction, and decreased the coercivity. Annealing at 580 °C increased the maximum permeability by 72.5%. The result of annealing at 580 °C shows that the ferromagnetic resonance frequency increased from 2 kHz for conventional epoxy resin coated samples to 80 kHz for the silicone resin insulated composites.     

A novel method determining longitudinally induced magnetic anisotropy in amorphous and nanocrystalline soft materials

In ferromagnetic amorphous and nanocrystalline soft magnetic alloys the induced magnetic anisotropy plays a fundamental role in the hysteresis behavior but, due to the elongated shape, it can be measured only if K_U is perpendicular to the sample long axis. In order to measure the longitudinal induced anisotropy, an original method derived from known thin layers measurement techniques was used. Hysteresis loops shifted by perpendicular bias field were recorded for this purpose. Direct measurement of the longitudinal induced anisotropy in amorphous and nanocrystalline ribbons or wire without needing sample preparation is reported for the first time. Evidence of self-induced anisotropy is brought in a Fe–Co-based nanocrystalline alloy.     

State-independent hypothesis to model the behavior of magnetic materials

The problem of modeling the magnetic behavior due to a magnetization process is usually dealt with using the classical scalar Preisach model (CSPM). Recently, it has been shown that in the case of soft magnetic materials better results can be obtained by means of the modified scalar Preisach model (MSPM). The problem of model identification is common to both these two approaches. In the past we used a Lorentzian approximation for CSPM identification. In this paper, after reviewing the method, which allows, in particular, the efficient determination of the parameters controlling the reversible magnetization, we propose an extension of the Lorentzian approximation to the case of MSPM identification. It will be shown that an accurate estimation of the model parameters is possible also in this case, as it is confirmed by comparing the model with experimental data.     

从磁滞回线了解铁磁性材料的性能

从磁滞回线简要讨论了铁磁性材料的性能及特点,并指出一些大学物理教材在这方面讨论的不妥之处.     

Comparison of the soft magnetic properties of permalloy and conetic thin films

The soft magnetic properties of the substrate/[non-buffer or buffer Ta]/[permalloy (Ni₈₀Fe₂₀) or conetic (Ni₇₇Fe₁₄Cu₅Mo₄)]/Ta prepared by ion beam sputter deposition are investigated. The value of the surface resistance of the conetic film is twice as high as that of the permalloy film. The value of the coercivity and magnetic susceptibility of the conetic film decreased by 25% and doubled relative to that of the permalloy film. The coercivity, with a value of 0.12 Oe, and the magnetic susceptibility, with a value of 1.2×10⁴ for the conetic film, are suitable for soft magnetic biosensor applications.     

Thickness dependence of microwave magnetic properties in electrodeposited Fe-Co soft magnetic films with in-plane anisotropy

In this work, the thickness effect of Fe₅₂Co₄₈ soft magnetic films with in-plane anisotropy on static and microwave magnetic properties was investigated. The hysteresis loop results indicated that the static in-plane uniaxial anisotropy field increased from almost 0-60 Oe with increasing film thickness from 100 to 540 nm and well-defined in-plane uniaxial magnetic anisotropy can be obtained as the thickness reached 540 nm or larger. Based on Landau-Lifshitz-Gilbert (LLG) equation, the microwave complex permeability spectra were analyzed and well fitted. The LLG curve-fitting results indicated that the initial permeability increased from 106 to 142 and the resonant frequency was shifted from 4.95 to 4.29 GHz as the film thickness was varied from 540 to 1500 nm. Moreover, it was found that there was a discrepancy between the static and the dynamically determined anisotropy field, which can be explained by introducing an additional effective isotropic ripple field. The decreased ripple field was suggested to result in a significant decrease of damping coefficient from 0.109 to 0.038.     

Structure and magnetic properties of FeSiAl-based soft magnetic composite with AlN and Al2O3 insulating layer prepared by selective nitridation and oxidation

FeSiAl is widely used in switching power supply, filter inductors and pulse transformers. But when used under higher frequencies in some particular condition, it is required to reduce its high-frequency loss. Preparing a homogeneous insulating coating with good heat resistance and high resistivity, such as AlN and Al₂O₃, is supposed to be an effective way to reduce eddy current loss, which is less focused on. In this project, mixed AlN and Al₂O₃ insulating layers were prepared on the surface of FeSiAl powders after 30 min exposure at 1100 °C in high purity nitrogen atmosphere, by means of surface nitridation and oxidation. The results revealed that the insulating layers increase the electrical resistivity, and hence decrease the loss factor, improve the frequency stability and increase the quality factor, especially in the high-frequency range. The morphologies, microstructure and compositions of the oxidized and nitrided products on the surface were characterized by Scanning Electron Microscopy/Energy Disperse Spectroscopy, X-Ray Diffraction, Transmission Electron Microscopy, Selected Area Electron Diffraction and X-ray Photoelectron Spectroscopy.     

Effects of soft layer softness on the magnetic properties of perpendicular exchange-coupled nanocomposite films

The anisotropy of the soft layer in the Co_100−xPt_x/Co₇₁Pt₂₉ (x=0, 7 and 17) perpendicular exchange-coupled composite (ECC) films was varied by changing the Pt content. The effects of soft layer softness (thickness and anisotropy) on the coercivity and magnetization reversal mechanisms of ECC were studied. Results showed that both remanence ratio (M_r/M_s) and coercivity of the ECC films reduced with an increase in soft layer thickness. However, the rate of coercivity reduction reduced when soft layer anisotropy was increased simultaneously. This was confirmed by the following facts. For the ECC with Co soft layer, the magnetization reversal mechanism within the ECC grains changed from coherent rotation to domain wall motion when soft layer thickness was changed from 2 to 15 nm. The impact of soft layer thickness on the magnetization reversals of the ECC grains reduced with an increase in soft layer anisotropy. On the other hand, the change of soft layer easy axis direction could possibly change the reversal mechanism of the ECC grains. The above experimental results showed that the coercivity of ECC film was controlled by the reversal mechanism inside the ECC grains.     

High-frequency magnetic properties of soft magnetic cores based on nanocrystalline alloy powder prepared by thermal oxidation

FeSiBNbCu nanocrystalline alloy powder was thermally oxidized in an air atmosphere to enhance an oxide layer formation on the surface of the powder and subsequently toroidal shape FeSiBNbCu nanocrystalline alloy powder cores were prepared by compaction at room temperature. The phase change on the surface of FeSiBNbCu nanocrystalline alloy powder by thermal oxidation was analyzed and its effect on the high frequency magnetic properties of the compacted cores was investigated. By thermal oxidation, the formation of the oxide layer consisting of Fe₂O₃, CuO, and SiO₂ on the surface of FeSiBNbCu nanocrystalline alloy powder was enhanced and the thickness of oxide layer could be controlled by changing the thermal oxidation time. FeSiBNbCu nanocrystalline alloy powder core prepared from the powder treated by thermal oxidation exhibits a stable permeability up to high frequency range over 10 MHz. The core loss could be reduced remarkably and the dc-bias property could be improved significantly, which were due to the formation of oxide layer consisting of Fe₂O₃, CuO, and SiO₂ on the FeSiBNbCu nanocrystalline alloy powder. The improvement in high-frequency magnetic properties of the FeSiBNbCu nanocrystalline alloy powder cores could be attributed to the effective electrical insulation by oxide layer between the FeSiBNbCu nanocrystalline alloy powders.     

Soft magnetic moldable composites: Properties and applications

A new type of electromagnetic soft magnetic material (SMM) is introduced, based on spherical iron powder particles and a suitable polymer binder. A key feature of this material is that it can be cast or molded into almost any 3D shape, hence the denotation soft magnetic moldable composite (SM²C). The SM²C is compared with a set of reference materials, such as ferrites, laminated steels, and soft magnetic composites, in terms of primary properties such as permeability and loss, and other properties, such as thermal conductivity and manufacturability. The SM²C has the obvious disadvantage of relatively low permeability, but offers benefits such as relatively low losses and high potential for close integration into electromagnetic circuits. Some recent SM²C applications are illustrated, and design and manufacturing aspects are discussed.     

Connection between microstructure and magnetic properties of soft magnetic materials

The magnetic behavior of soft magnetic materials is discussed with some emphasis on the connection between macroscopic properties and underlying micromagnetic energy aspects. It is shown that important conceptual gaps still exist in the interpretation of macroscopic magnetic properties in terms of the micromagnetic formulation. Different aspects of hysteresis modeling, power loss prediction and magnetic non-destructive evaluation are discussed in this perspective.     

Effect of thermal process on magnetic anisotropy in FeCoB soft underlayer

Relationship between magnetic anisotropy field H_k and thermal processes during the preparation has been studied for FeCoB thin films. The FeCoB films deposited on the glass substrates by facing targets sputtering successfully showed strong magnetic anisotropy when the substrate was heated at the substrate temperature T_s above 100 °C. Additionally, the lattice spacing of FeCo(1 1 0) in the perpendicular direction was found to decrease depending on the substrate temperature T_s. Among various temperature histories, the heating processes with a phase of increasing T_s revealed the further improvement of H_k. Meanwhile, high H_k in the films disappears after the post-deposition annealing at the temperature above 400 °C.     

Microstructure and magnetic property of electroless-plated CoNiFeB soft underlayer

An electroless-plated CoFeNiB film as a soft underlayer in perpendicular magnetic recording is studied by magneto-optical Kerr effect microscope, magnetic force microscopy (MFM), and transmission electron microscopy. A stray field is evidently suppressed for the anisotropic CoFeNiB film, which is under an applied field during the plating process. The lines of magnetic flux show that the Ni seed layer have no intrinsic effect on the homogenous magnetic state of the CoFeNiB layer. The interaction between a MFM tip and the CoFeNiB layer is clearly observed by electron holography indicating the excellent soft magnetic properties required by the soft underlayer.     

Microwave magnetic properties of soft magnetic thin films

We review our works that focus on the microwave magnetic properties of metallic,ferrite and granular thin films.Soft magnetic material with large permeability and low energy loss in the GHz range is a challenge for the inforcom technologies.GHz magnetic properties of the soft magnetic thin films with in-plane anisotropy were investigated.It is found that several hundreds of permeability at the GHz frequency was achieved for Co100-xZrx and Co90Nb10 metallic thin films because of their high saturation magneti...     

A new ferromagnetic hysteresis model for soft magnetic composite materials

A new ferromagnetic hysteresis model for soft magnetic composite materials based on their specific properties is presented. The model relies on definition of new anhysteretic magnetization based on the Cauchy-Lorentz distribution describing the maximum energy state of magnetic moments in material. Specific properties of soft magnetic composite materials (SMC) such as the presence of the bonding material, different sizes and shapes of the Fe particles, level of homogeneity of the Fe particles at the end of the SMC product treatment, and achieved overall material density during compression, are incorporated in both the anhysteretic differential magnetization susceptibility and the irreversible differential magnetization susceptibility. Together they form the total differential magnetization susceptibility that defines the new ferromagnetic hysteresis model. Genetic algorithms are used to determine the optimal values of the proposed model parameters. The simulated results show good agreement with the measured results.