Soft Ferrites Research Articles

Observation of the magnetic entropy change in Zn doped MnFe2O4 common ceramic: Be cool being environmental friendly

We report the detail investigation on the magnetic and magnetocaloric behaviour of polycrystalline Mn1-xZnxFe2O4 (0.0 ≤ x ≤ 0.7) ferrite. The magnetization analysis shows that the increase of Zn concentration in the samples results in decrease of saturation magnetization. The maximum magnetic entropy change, |ΔSMmax| is evaluated through M-H isotherms measurements and takes values of 1.25, 1.11, 1.07, and 0.64 Jkg−1K−1 for x = 0.0, 0.3, 0.5, and 0.7, respectively under a maximum applied magnetic field of 2.5 T. The corresponding relative cooling power (RCP) for these samples were found to be 102, 162, 96, and 89 Jkg-1 for x = 0.0, 0.3, 0.5, and 0.7, respectively. After the comparison of the obtained values of |ΔSMmax| and RCP with those reported earlier for the other compounds, recommend to explore such common soft ferrites based materials for magnetic refrigeration.

Achieving Excellent Strength‐Ductility Balance and Lower Yield Ratio in a 690 MPa‐Grade Multiphase Construction Steel

In this article, thermomechanical controlled processing (TMCP) plus tempering (T) is adopted to acquire a novel 690 MPa‐grade high‐strength low‐carbon bainitic construction structural steel, which has an optimum balance of strength‐ductility and lower yield ratio (YR). The results show that the as‐rolled steel consists of bainitic ferrite, lath‐like bainite, and granular bainite. With an increase in the tempering temperature, a great deal of carbonitrides precipitates and maintains a small nano‐scaled size without coarsening. Their interaction with dislocations induces an increase in strength. When the tempering temperature further increases, some grain boundaries between adjacent bainitic laths gradually blur or even disappear, and the average width of the bainitic laths increases to ≈860 nm. The recovery of bainitic laths is the main reason for the decreased strength. Due to the synergistic effect of the small dot‐shaped martensite/austenite (M/A) constituents and grain boundaries misorientation distribution, maximum impact absorbed energy is achieved after tempered at 500 °C. Furthermore, the lower YR is achieved by appropriate control of strength difference between the soft bainitic ferrite and hard M/A constituents via tempering.

Effect of Bi2O3 contents on magnetic and electromagnetic properties of LiZnMn ferrite ceramics

Soft LiZnMn ferrites with low coercive force values and small grain sizes were developed by the solution combustion synthesis and low temperature sintering technique for microwave applications at a high frequencies. Bismuth oxide was used as an additive to lower the sintering temperature. The examination covered the influence of Bi2O3 on the crystal structure, microstructure, primary magnetic and dielectric characteristics of lithium-zinc-manganese ferrites. The most promising sample designed for using in microwave devices was produced by sintering at 1075 ℃ temperature for 8 h with added 1.5 wt% Bi2O3. These production conditions have yielded 2.98 µm average grain size in a ceramic product, the density is 4.84 cu cm/g, and the coercive force, residual induction, and saturation induction are 58 A/m, 2078.4 G, and 3439.1 G, respectively. In addition, this sample demonstrates a high initial magnetic permeability (μi = 168), Curie temperature (Tc = 437.5 ℃), high values of the dielectric loss tangent (tan δɛ = 6.32⸱10−3), ferromagnetic resonance line width (ΔH = 280 Oe) and the resonance line of spin waves (ΔHk = 1.87 Oe). Further increase in the bismuth oxide content allows observing a change in the ceramics microstructure, accompanied by a deterioration in the magnetic and electromagnetic characteristics. Here, the discussion covers the mechanism of change in the functional properties of lithium-zinc-manganese ferrites produced in the conditions of solution combustion with added bismuth oxide. Thus, synthesizing of initial pre-ceramic powder by glycine-nitrate combustion and subsequent low-temperature sintering with added bismuth oxide is a novel efficient technique of producing advanced soft high-frequency LiZnMn ferrites.

On the anhysteretic magnetization of soft magnetic materials

Electrical steels are still the materials of choice for large-scale transformers and most electric motors. Yet, they may present a nonhomogeneous magnetic nature which prevents describing accurately their anhysteretic magnetization with the Langevin-Weiss model. Although interpolation and extrapolation methods may be used to model any anhysteretic curve, a simple and physically-based model would be of great value for fundamental and applied research. Inspired in the law of partial volumes for gas mixtures, we proposed a law of partial magnetizations for magnetic mixtures. In a two-component system, the model leads to the double Langevin-Weiss function. We also introduced a graphical method and a fitting approach to analyze and model anhysteretic magnetization curves. A semi-log magnetization derivative plot is central to this end. We validated our strategy through well-motivated examples using published data on soft magnets. The single Langevin-Weiss function provided an accurate description of the magnetization of isotropic and anisotropic magnetically homogeneous materials: a soft ferrite and a nanocrystalline alloy, respectively. For modelling a magnetization transverse to the material’s preferred direction, the key is to allow a negative molecular field constant. The double Langevin-Weiss function was suitable for less homogeneous materials, such as a grain-oriented electrical steel magnetized along the rolling direction and a non-oriented electrical steel. Moreover, a highly-grain-oriented electrical steel magnetized transverse to the rolling direction, which exhibits a constricted hysteresis loop, could be modeled in excellent agreement with data. The key for the latter, has been to allow an antiparallel arrangement of the mean magnetization of both components.

Green synthesis based X-type Ba–Zn Hexaferrites: Their structural, Hysteresis, Mӧssbauer, dielectric and electrical properties

Ba2Zn2Fe28O46 hexaferrite was prepared using green synthesis with different quantities of ginger root extract (obtained from 0.0, 17.5, 35, 52.5 and 70 g of ginger root) as a natural antioxidant reducing agent. The dried precipitates were preheated at 550 °C/4 h and finally heated at 1200 °C/5 h. The effect of ginger root extract on structural, phase purity, magnetic, Mӧssbauer and low frequency (10 Hz–2 MHz) dielectric properties were investigated. XRD analysis of samples prepared with extracts from 35, 52.5, and 70 g of ginger depicted pure X-phase, while the other samples (0.0, 17.5 g) showed the secondary phase of M-type (BaM, BaFe12O19) along with hematite (12% α-Fe2O3). Hence, samples with greater amounts of ginger extract formed single-phase X-type hexaferrite. Saturation magnetization (MS) varied from 40.8 A m2/kg without ginger extract to 69.8 A m2/kg with extract from 52.5 g ginger, and was <65 A m2/kg for all samples made with the ginger extract. All synthesized samples were relatively soft ferrites, and coercivity increased with amount of ginger extract used. The Mӧssbauer spectra explored six sextets of five magnetic sub-lattices, and the presence of Fe3+ (99.4–97.3 %) and Fe2+ (0.6–2.7 %) ions, with more Fe2+ present in the extract-derived samples. The variations in MS based on hysteresis loops were in agreement by Mössbauer spectroscopy. The use of the extract also significantly reduced the grain size, from 3.3 μm without ginger extract to 0.7–1.7 μm with the extract, with a corresponding increase in coercivity from 16 to 40–80 kA/m. The samples prepared with extracts from 35 g to 52.5 g ginger root possessed considerable real dielectric constant compared to the others, but the extract also increased conductivity in the high-frequency region. Complex impedance displayed low values in the high-frequency region, and Cole-Cole plots revealed that the main contribution to conductivity in extract-based samples was from the grains. The reducing action of the green extract not only produced single phase X ferrite, but it also reduced grain size to ∿1–2 μm and greatly increased MS.

Structural, optical, electrical, dielectric, molecular vibrational and magnetic properties of La3+ doped Mg–Cd–Cu ferrites prepared by Co-precipitation technique

Ferrites are among the most frequently investigated materials mainly due to interesting and practically different properties. Therefore, easily and cost-effective lanthanum doped Mg0.5Cd0.25Cu0.25Fe2-xLaxO4 (x = 0.0, 0.0125, 0.025, 0.0375 and 0.05) ferrites were synthesized by a co-precipitation route, a comprehensive characterisation of their structural, optical, electric, dielectric, molecular vibrational, and magnetic properties were carried out. X-ray diffraction analysis confirmed the formation of a cubic spinel structure. Variations in frequency bands were also observed with amplification in optical band gap energy (2.95 – 3.38 eV) due to La3+ ions insertion. The electric resistivity had opposite trends at low and high temperatures with increasing La3+ content. The Curie temperature, activation energy, and drift mobility were also determined to have values consistent with the semiconducting behavior of the soft ferrites. The saturation magnetization (MS) has a maximum value 49.385 emu/g with remanent magnetization (Mr) was 34.928 emu/g and coercivity 661.4 Oe for La3+ concentration x = 0.05. The minimum dielectric loss was observed for La3+ concentration x = 0.025. Moreover, the resistivity (ρ) has a maximum value of 7.95 × 104 Ω cm for La3+ concentration x = 0.025. The calculated frequency range of La3+ doped Mg–Cd–Cu ferrites was detected in the microwave range (3.36 – 10.80 GHz), suggesting the potential application of the materials in longitudinal recording media and microwave absorbance.

Methods of Controlling the Microwave Absorption Properties of Soft Ferrite in the X-Band Range

Methods of Controlling the Microwave Absorption Properties of Soft Ferrite in the X-Band Range

The magnetic properties dependence on temperature of Li-ferrite nanoparticle

The chemical formula Li0.5Fe2.5O4 of lithium ferrite prepared by two different chemical methods mentioned as low temperature solid state reaction (LTSSR) and modified combustion method (MCM). The samples showed nanoparticle scale with spinal structure. The magnetic analyses have done by the vibrating sample magnetometer VSM device, and both samples have the same magnetic properties represented by the magnetic saturation, remanence magnetization, and coercive magnetic field. The shape of hysteresis loop showed a soft ferrite and its area decreased with temperature increasing. On the other hand, the magnetic susceptibility decreased with increasing temperature for both samples of ferrite Li0.5Fe2.5O4 prepared. The sample of LTSSR exhibited a magnetic moment of about 0.410-3 JT-1 at applied magnetic field 50 kOe which is approaching the same for the sample prepared by MCM method.

Soft Magnetic Nanocrystalline Ni-Fe-X-Y and MeFe2O4 Powders Obtained by Mechanosynthesis

"The soft magnetic nanocrystalline powders, alloys (Ni3Fe, 79Ni16Fe5Mo, 77Ni14Fe5Cu4Mo, wt. %) and zinc ferrite, were obtained by dry and wet mechanical alloying and reactive milling, followed by different heat treatments. The powders were characterised by X-ray diffraction, scanning electron microscopy, X-ray microanalysis, differential scanning calorimetry, thermomagnetic and magnetic measurements. The X-ray diffraction shown the progressive new phases formation. The crystallite size is between 18-7 nm depending on materials and milling conditions. The particle size is smaller for wet-mechanical alloying comparing with dry-milling. The thermomagnetic measurement shown the Curie temperature of the alloys. The spontaneous magnetisation of the wet-milled and annealed samples is higher than of the molten alloys. Keywords: mechanical alloying; Ni-Fe-X-Y alloys; soft ferrite; magnetisation; XRD; DSC. "

Frequency dispersion model of the complex permeability of soft ferrites in the microwave frequency range

AbstractThe complex permeability of Cu‐doped nickel‐zinc polycrystalline ferrites is strongly dependent on microstructure, particularly, on relative density () and average grain size (). In this study, a mathematical model, able to fit the measured magnetic permeability spectra from 106 to 109 Hz, is proposed and validated for a width range of average grain sizes (3.40–23.15 μm) and relative densities (0.83–0.96). To the authors’ knowledge, domain‐wall motion and spin rotation contributions to magnetic permeability have been integrated jointly with the microstructure for the first time in the proposed model, highlighting the relative influence of each magnetizing mechanism and microstructure on the magnetic permeability at different angular frequencies.

Tailoring Heterogeneous Microstructure in a High-Strength Low-Alloy Steel for Enhanced Strength-Toughness Balance

The attainment of both strength and toughness is of vital importance to most structural materials, although unfortunately they are generally mutually exclusive. Here, we report that simultaneous increases in strength and toughness in a high-strength low-alloy (HSLA) steel were achieved by tailoring the heterogeneous microstructure consisting of soft intercritical ferrite and hard martensite via intercritical heat treatment. The heterogeneous microstructure features were studied from the perspective of morphology and crystallography to uncover the effect on mechanical properties. Specifically, the volume fraction of martensite increased with increasing annealing temperature, which resulted in increased back stress and effective stress, and thereby an improved strength-ductility combination. The enrichment of carbon and alloying elements in the martensite was lowered with the increase in annealing temperature. As a result, the hardness difference between the intercritical ferrite and martensite was reduced. In addition, the globular reversed austenite preferentially grew into the adjacent austenite grain that held no Kurdjumov-Sachs (K-S) orientation relationship with it, which effectively refined the coarse prior austenite grains and increased the density of high angle grain boundaries. The synergy of these two factors contributed to the improved low-temperature toughness. This work demonstrates a strategy for designing heterostructured HSLA steels with superior mechanical properties.

Electronic, magnetic, and microwave properties of hard/soft nanocomposites based on hexaferrite SrNi0.02Zr0.02Fe11.96O19 with variable spinel phase MFe2O4 (M = Mn, Co, Cu, and Zn)

Hard/soft nanocomposites (NCs) of SrNi 0.02 Zr 0.02 Fe 11.96 O 19 (SrNiZr)/MFe 2 O 4 (M = Mn, Co, Cu, and Zn) were prepared using a one-pot sol-gel auto-combustion technique. All produced samples showed smooth M − H curves and single peaks on the dM/dH against H curves. This indicates that complete exchange-coupled effects between phases were achieved. Furthermore, the squareness ratio SQR=(M r /M s ) was obtained and found to be higher than 0.5 at 300 K. This refers to the occurrence of excellent exchange coupling behavior among the soft and hard ferrites, and their structures consist of a single magnetic domain. The electrodynamic parameters were investigated in the 2–18 GHz frequency band using a coaxial line. The dependences of the real and imaginary parts of μ and ε as a function of frequency were determined from the measured S-parameters. A strong correlation between the chemical composition of the soft magnetic phase and the electrodynamic parameters of the composite was observed. This was analyzed in terms of the atomic weight and configuration of the electronic shells of the A-cation in the soft phase. The electromagnetic absorption (EMA) of the investigated composites was estimated from the reflection losses calculated from μ and ε. The maximal EMA value was observed.

Liquid metal enabled continuous flow reactor: A proof-of-concept

Liquid metal enabled continuous flow reactor: A proof-of-concept

Iron-Oxide Magnetic Materials for Millimeter-Wave Absorption

High-performance electromagnetic-wave absorbers are required for the control of millimeter-wave spectra, which will play a big role in future 5G and 6G wireless networks. Traditional absorbing materials comprised of metals or soft ferrites have been developed but their lack of ability to absorb at extremely high frequencies continues to hinder their practical applications. Thus, this article briefly introduces several iron-oxide magnetic materials with millimeter-wave absorbing capability.

Mimicking Barkhausen noise measurement by in-situ transmission electron microscopy - effect of microstructural steel features on Barkhausen noise

A relationship between microstructural steel features and an outcome of the Barkhausen noise (BN) measurement was studied. Two different microstructures, martensite and pearlite-ferrite were used. Commonly, BN is linked directly to the sample hardness. A BN outcome from both martensite and pearlite-ferrite was, however, similar even though martensite has three times higher hardness. To reveal the connection between microstructural features and BN, a typical industrial BN measurement was mimicked by in-situ transmission electron microscopy (TEM). Martensite needed higher field strength to move domain walls (DWs) than pearlite-ferrite. In martensite, DWs gathered to areas with high dislocation density. Fe3C lamellae in pearlite were strong pinning sites. DWs perpendicular and parallel to martensite laths started to move with the same field strength value. In pearlite, DWs perpendicular to lamellae started to move before the parallel ones. The RMS envelope of ferrite-pearlite starts earlier than that of martensite due to soft ferrite. Magnetically harder pearlite probably caused “a tail” and the envelope ends almost at the same time with martensite. . Nevertheless, similar peak width values were found for both samples. Martensite and pearlite have a lot of strong pinning sites, dislocations and Fe3C, respectively. Fe3C density is not as high as dislocation density. Ferrite has strong pinning sites only at low incidence, but as known, huge BN information volume compared to martensite and pearlite. This resulted in the similar pulse count from martensite and ferrite-pearlite.

Electrical and dielectric properties of rare earth substituted hard-soft ferrite (Co0.5Ni0.5Ga0.01Gd0.01Fe1.98O4)x/(ZnFe2O4)y nanocomposites

ZnFe2O4 (ZFO) NPs (nanoparticles), Co0.5Ni0.5Ga0.01Gd0.01Fe1.98O4 (CNGaGdFO) NPs and hard-soft spinel ferrite (H/S) (CNGaGdFO)x/(ZFO)y (x:y = 1:1, 1:2, 1:3, 2:1, 3:1 and 4:1) NCs (nanocomposites) were synthesized via a one-pot sol–gel auto combustion route. X-ray powder diffraction (XRD) analyses confirmed the purity of ZFO NPs, CNGaGdFO NPs and H/S (H/S) (CNGaGdFO)x/(ZFO)y (x:y = 1:1, 1:2, 1:3, 2:1, 3:1 and 4:1) (absence of any second phase). The crystallite size of NCs was between 39 and 52 nm. The cubic morphology was observed for ZFO NPs, CNGaGdFO NPs and all H/S NCs by the help of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. Energy dispersive X-Ray analysis (EDX) also confirmed the chemical formula of all the NC samples. Electrical and dielectric properties of ZFO NPs, CNGaGdFO NPs and H/S NCs were explored with an impedance analyzer with f ≤ 3.0 MHz, where f stands for frequency, and within the temperature range between 20 and 120 °C. Electric and dielectric parameters such as AC conductivity as well as DC conductivity, activation energy, dielectric constant, dielectric loss in addition to the dissipation parameter relevant to the electrical energy due to different physical processes were measured for each of the given compositional ratios. The AC conductivity was found to follow the frequency-dependent power law in general, being mainly reliant on the compositional ratios and the measured temperatures especially at lower frequencies. This study has shown that CoNiGaGdFeO-ZnFe2O4 H/S NCs carry out conduction mechanisms, which can be predominantly credited to grain–grain boundaries for various compositional ratios. The dielectric constant of (CNGaGdFO)x/(ZFO)y (x:y = 1:1, 1:2, 1:3, 2:1, 3:1 and 4:1) H/S NCs indicates common dielectric behaviours with frequency, largely dependent on compositional rates of the hard to soft spinel ferrites. It is observed that hard ferrite is dominant in the formation of the semicircles, and the diameter of the semicircles shows a drop as the temperature rises, suggesting a temperature-dependent relaxation mechanism. Consequently, the observed variation of the studied dielectric parameters with frequency can be explained by the conduction mechanism in most composition ratios of hard to soft spinel ferrites, which can be explained by a phenomenological method with Koop's model.

On the modelling of the anhysteretic magnetization of homogeneous soft magnetic materials

The analysis and optimization of devices with soft magnetic cores, such as inductive sensors and electric machines, rely on a simple and precise modelling of their nonlinear anhysteretic magnetization. The Langevin-Weiss equation of state has the advantages of being physically-based and capable of accurately describing isotropic materials. In fact, it has even been adopted as the backbone of the popular Jiles-Atherton model to describe magnetic hysteresis. However, many studies show the difficulty of retrieving the modelling parameters given an experimental anhysteretic curve, for which stochastic optimization methods are generally used.In this work, we present a simple and deterministic method for finding the parameters of the Langevin-Weiss model: the saturation magnetization, the temperature dependent a parameter, and the molecular field constants. To this end, we optimize a problem with a nonlinear solver where the fitting variables are instrinsically bounded. We validated the approach by analyzing three widely used soft magnets; a grain-oriented silicon steel, a Mn-Zn soft ferrite, and a Fe-based nanocrystalline alloy with induced anisotropy.We demonstrate that, contrary to what has previously been assumed, the Langevin-Weiss function can provide a good description of the anhysteretic magnetization of any homogeneous material, even materials with strong transverse uniaxial anisotropy. The key, which seems to have been overlooked, is to allow the Weiss molecular field to be negative.

An Improved Core Loss Model of Ferromagnetic Materials Considering High-Frequency and Nonsinusoidal Supply

With the emerging power electronic technologies, numerous electrical devices use high-frequency and nonsinusoidal supplies. Such sources generate complex harmonic fields that overburden the accurate prediction of core losses using the conventional finite element method (FEM). Thereby, to predict core losses under those high-frequency and nonsinusoidal supplies accurately, this study first built a test system for core losses measurement of ferromagnetic materials (e.g., soft ferrite, laminated steels, and nanocrystalline alloy) fed by the square and pulsewidth modulated (PWM) supplies. Then, the loss prediction problems of the classical core loss model under high-frequency and nonsinusoidal supplies are revealed. Afterward, an improved FEM-based core loss model is proposed, which includes a piecewise variable parameters based hysteresis loss model, an eddy current loss model considering different cross sections of magnetic circuit and supply waveforms, and improved excess loss coefficients. Experimental validations on different materials, the nanocrystalline alloy in an 11-kVA intermediate frequency transformer, the ultrathin silicon sheets in a 10-kW high-speed permanent magnet motor, and the nanocrystalline alloy in a 3-kW wireless power transfer system, are conducted systematically. The effectiveness and generality of the improved core loss model were verified.

Study the electrical and magnetic properties of Ferrite Ni1-x ZnxFe2O4 films and their potential use in the magnetic core of transformers

Membranes (Ni1-x ZnxFe2O4) were prepared by chemical precipitation method and with different weight ratios of values (x = 0, 0.3, 0.5, 0.7, 0.9), the electrical properties of the prepared samples were studied with the presence of a magnetic field of magnitude (0.45T), the result (Hall Effect) The majority of charge carriers are electrons, while the results of magnetic tests showed that the prepared films of different weights are of a type (soft Ferrite) The membranes behaved as a ferromagnetic material. The results indicate that the membranes can be used in the fields of microwave frequencies and in the transformers inside the magnetic core due to the smallness of the hysterical loop.

Determining role of heterogeneous microstructure in lowering yield ratio and enhancing impact toughness in high-strength low-alloy steel

Here we present a novel approach of intercritical heat treatment for microstructure tailoring, in which intercritical annealing is introduced between conventional quenching and tempering. This induced a heterogeneous microstructure consisting of soft intercritical ferrite and hard tempered martensite, resulting in a low yield ratio (YR) and high impact toughness in a high-strength low-alloy steel. The initial yielding and subsequent work hardening behavior of the steel during tensile deformation were modified by the presence of soft intercritical ferrite after intercritical annealing, in comparison to the steel with full martensitic microstructure. The increase in YR was related to the reduction in hardness difference between the soft and hard phases due to the precipitation of nano-carbides and the recovery of dislocations during tempering. The excellent low-temperature toughness was ascribed not only to the decrease in probability of microcrack initiation for the reduction of hardness difference between two phases, but also to the increase in resistance of microcrack propagation caused by the high density of high angle grain boundaries.