Commercial Ferrites Research Articles

Cold sintering assisted processing of Mn-Zn ferrites

Typically, commercial Mn-Zn ferrites are sintered at high temperatures with prolong times. In this work, commercial Fe2O3-rich ferrite powders with the composition of 0.21Mn0.8Zn0.2Fe2O4-0.79Fe2O3 (wt%) are densified by cold sintering at 300 °C with the assistance of organic salts, including MnC2O4·2H2O, FeC2O4·2H2O, and Zn(C2H3O2)2·2H2O. Excessive Fe2O3 enters into spinel structure forming a solid solution through annealing in low pO2 at 1350 °C. The sintering behaviors, microstructures, magnetic properties and impedances are investigated. The dehydration of organic salts provides mediate liquid phase to trigger the dissolution-precipitation process, which assists the densification of ceramics. The grains grow from 0.15 µm to 0.52 µm and 7.67 µm after cold sintering at 300 °C and annealing at 1350 °C, respectively. The initial permeability of cold sintered sample is improved to 11000 with a Curie temperature of 125 °C. This work provides a feasible route for cold sintering assisted processing of commercial soft magnetic ferrites.

Epitaxy growth of pure phase CeFeO3 thin films with high magneto-optical performance and strong vertical magnetic anisotropy

The magneto-optical effects of rare earth ferrite can be greatly improved by doping Ce3+ ions. CeFeO3 with high Ce3+ concentration has excellent magneto-optical properties in theory. And due to its perovskite structure it is more suitable to be deposited on the substrates of optical devices compared with the commercial garnet ferrite. In this paper, the pure phase CexFe2–xO3 films were successfully obtained on the quartz glass and <100>-oriented SrTiO3 crystal substrates by radio frequency magnetron sputtering. The effects of substrate and Ce:Fe ratio on the epitaxial orientation, magnetism and magneto-optical performance of films were systematically studied. For the Ce1.0Fe1.0O3/STO film, its MCD ellipticity (ψF) intensity can reach up to 4750(°)/cm in the visible band and 14090(°)/cm in near ultraviolet band. And it also shows a strong vertical magnetic anisotropy, which makes it maintain a good thermal stability when the device size is reduced. These mean that the Ce1.0Fe1.0O3/STO film has a promising application in integrated optical communication devices.

Magnetic Losses in Soft Ferrites

We review the basic phenomenology of magnetic losses from DC to 1 GHz in commercial and laboratory-prepared soft ferrites considering recent concepts regarding their physical interpretation. This is based, on the one hand, on the identification of the contributions to the magnetization process provided by spin rotations and domain walls and, on the other hand, the concept of loss separation. It additionally contemplates a distinction between the involved microscopic dissipation mechanisms: spin damping and eddy currents. Selected experimental results on the broadband behavior of complex permeability and losses in Mn-Zn ferrites provide significant examples of their dependence on sintering methods, solute elements, and working temperature. We also highlight the peculiar frequency and temperature response of Ni-Zn ferrites, which can be heavily affected by magnetic aftereffects. The physical modeling of the losses brings to light the role of the magnetic anisotropy and the way its magnitude distribution, affected by the internal demagnetizing fields, acts upon the magnetization process and its dependence on temperature and frequency. It is shown that the effective anisotropy governs the interplay of domain wall and rotational processes and their distinctive dissipation mechanisms, whose contributions are recognized in terms of different loss components.

Co-based magnetic nanostructured material for high frequency applications

The RF circuits are difficult to be miniaturized without compromises concerning the technical performances. The inductors and antennas are the major constraints for systems miniaturization, due to the lack of magnetic materials with adequate high frequency properties. The paper presents novel Co-based magnetic nanostructured materials, with improved characteristics which recommend them as potential candidates for transformers and inductors in electronic components: higher level for saturation magnetisation and electric resistivity in comparison with commercial ferrites. The magnetic nanocomposites are prepared by sol-gel route and consist on Co magnetic nanocrystallites, arranged in a crystalline matrix (silicates, for example). The main physical characteristics of the Co/SiO2 nanopowders are developed after appropriate calcination and annealing, being dependent on the SiO2 amount and on the thermal treatment parameters: saturation magnetisation Ms = 81.7 – 130.4 emu/g, coercivity Hc = 21.7 – 26.9 kA/m (273 - 338 Oe) and increased resistivities for the sintered samples, due to the presence of the SiO2 layers.

Exploration of the 3-D Printing of Transformer Structures With Embedded Ferrite Cores

For inductor and transformer circuit components that operate at higher frequencies, the existence of parasitic capacitance due to the winding structure determines the device's self-resonance frequency. It is desirable to have precise design and manufacturing control over the winding structure to properly control this capacitance for reduced manufacturing variability, suggesting lithographic or computer numerical controlled (CNC) fabrication. Lithographic or CNC methods, however, reduce the possible number of winding turns due to the high aspect-ratio of vias, limiting the device inductance. A 3-D printing technology offers the opportunity to increase the aspect-ratio limitation by fabricating only a thin layer at one time. In this paper, the process of 3-D printing transformer structures was explored with multiple variations. A Voxel8 printer was mostly used, with the ability to print plastic as well as conductive silver paste. Commercial and custom MnZn ferrites were used as core materials, as well as printed magnetic polylactic acid (PLA) plastic using a dual-extruder MAKEiT Pro-M printer. Windings were fabricated by either silver paste deposition interleaved with plastic layers or post-fabrication silver ink injection. It was found that interleaved silver paste deposition produced very low resistance windings (high quality factor inductor) when compared with injected silver ink but had a high probability of shorting windings. Injected silver ink windings were found to have higher reliability only when the parts are properly printed liquid tight. Inductances were in agreement with theoretical predictions for most fabricated devices, and resistances were much higher for injected silver ink windings than interleaved printed windings. The best broadband transformer performance, which is an optimal low winding resistance and high mutual inductance, was found for a 36 mm outer diameter, 23 mm inner diameter, and 10 mm-thick MnZn ferrite core with an eight-turn printed winding.

Cobalt-Based Ferrites Characterization Using Two Different Terahertz Time-Domain Spectrometers

We report an experimental study of the electrical properties of manganese cobalt (MnCo) and nickel cobalt (NiCo) ferrites in the terahertz (THz) frequency band. The study is motivated by the potential of MnCo, NiCo, and other magnetic ceramics for the fabrication of active and passive devices for THz wave communications. Using two different terahertz (THz) time-domain spectroscopy systems, we characterized the optical constants of cobalt ferrites doped with manganese and nickel in the technologically important 0.2–1 THz frequency band. The MnCo and NiCo ferrites investigated in our study exhibit a lower refractive index and absorption coefficient in the 0.2–1 THz frequency band than commercial strontium ferrite. We observed that using different valency ion oxide leads to a sudden change of the refractive index as a function of sample stoichiometries. Our experimental results provide evidence that microwave ferrite technology can be extended to the THz frequency band.

Magnetic nickel ferrite nanoparticles as highly durable catalysts for catalytic transfer hydrogenation of bio-based aldehydes

Commercial nickel ferrite (NiFe2O4) nanoparticles are efficient, durable and magnetically recoverable heterogeneous catalysts for catalytic transfer hydrogenation of biomass-derived furfural as well as other aldehydes with 2-propanol as the H-donor forming furfuryl alcohol and various aromatic/allyl/alkenyl alcohols, respectively.

NiCuZn Ferrite Cores by Gelcasting: Processing and Properties

We used gelcasting, a pressure-less processing technology for fabricating ceramic parts, to make NiCuZn ferrite cores, which are traditionally made by a process that requires high hydrostatic pressure. A commercial NiCuZn ferrite powder was mixed with water, dispersant, and organic monomers to form a slurry, and then cast it into a mold of toroid shape followed by sintering at 900 °C, 950 °C, and 1000 °C for two hours. The sintered core mass density was found to increase with sintering temperature. The magnetic properties of the cores, i.e., complex permeability and core-loss density, were measured. We found that the real part of the permeability increased with sintering temperature from about 44 at 900 °C to 78 at 1000 °C. The core-loss density data at 5 MHz showed that the cores sintered at 950 °C had the lowest core-loss density; approximately 50% lower than that of a commercial NiZn ferrite (4F1) core. Since gelcasting does not require pressure and is scalable and low cost, it has the potential to make magnetic cores with intricate shapes and sizes for desired coupling of magnetic fluxes to improve efficiency and power-density of power electronics converters.

Effect of calcination temperature of a copper ferrite synthesized by a sol-gel method on its structural characteristics and performance as Fenton catalyst to remove gallic acid from water

A copper ferrite synthesized by a sol–gel combustion method was calcined at different temperatures up to 800°C, determining changes in its structural characteristics and magnetic measurements and studying its catalytic performance in gallic acid removal by Fenton reaction. The main objective was to study the effect of the calcination temperature of copper ferrite on its crystalline phase formation and transformation, activity and metal ion leaching. The cubic-to-tetragonal transformation of the spinel occurred via its reaction with the CuO phase, displacing Fe3+ ions in B (octahedral) sites out of the spinel structure by the following reaction: 2Fe3+B+3CuO→Fe2O3+3Cu2+B. The catalysts showed superparamagnetic or substantial superparamagnetic behaviour. At higher calcination temperatures, catalyst activity was lower, and Cu ion leaching was markedly decreased. There was no Fe ion leaching with any catalyst. The as-prepared catalyst showed better catalytic performance than a commercial copper ferrite. Leached Cu ions acted as homogeneous catalysts, and their contribution to the overall removal mechanism was examined. Cu2O present in the as-prepared catalysts made only a small contribution to their activity. Finally, the reutilization of various catalysts was studied by performing different catalytic cycles.

Topotactic Synthesis of Porous Cobalt Ferrite Platelets from a Layered Double Hydroxide Precursor and Their Application in Oxidation Catalysis.

Monocrystalline, yet porous mosaic platelets of cobalt ferrite, CoFe2 O4 , can be synthesized from a layered double hydroxide (LDH) precursor by thermal decomposition. Using an equimolar mixture of Fe2+ , Co2+ , and Fe3+ during co-precipitation, a mixture of LDH, (FeII CoII )2/3 FeIII1/3 (OH)2 (CO3 )1/6 ⋅m H2 O, and the target spinel CoFe2 O4 can be obtained in the precursor. During calcination, the remaining FeII fraction of the LDH is oxidized to FeIII leading to an overall Co2+ :Fe3+ ratio of 1:2 as required for spinel crystallization. This pre-adjustment of the spinel composition in the LDH precursor suggests a topotactic crystallization of cobalt ferrite and yields phase pure spinel in unusual anisotropic platelet morphology. The preferred topotactic relationship in most particles is [111]Spinel ∥[001]LDH . Due to the anion decomposition, holes are formed throughout the quasi monocrystalline platelets. This synthesis approach can be used for different ferrites and the unique microstructure leads to unusual chemical properties as shown by the application of the ex-LDH cobalt ferrite as catalyst in the selective oxidation of 2-propanol. Compared to commercial cobalt ferrite, which mainly catalyzes the oxidative dehydrogenation to acetone, the main reaction over the novel ex-LDH cobalt is dehydration to propene. Moreover, the oxygen evolution reaction (OER) activity of the ex-LDH catalyst was markedly higher compared to the commercial material.

A method to decrease the harmonic distortion in Mn-Zn ferrite/PZT and Ni-Zn ferrite/PZT layered composite rings exhibiting high magnetoelectric effects

We have investigated the magnetoelectric (ME) effect in layered composite rings subjected to circumferential AC magnetic fields and DC magnetic fields in radial, axial, or circumferential directions. Bilayer samples were obtained combining different grades of commercial Mn-Zn ferrites or Ni-Zn ferrites with commercial lead zirconate titanate (PZT). Mn-Zn ferrites with low magnetostriction saturation (λs&amp;lt;10−6) and low magneto-crystalline anisotropy constants show high ME capabilities when associated with PZT in ring structures. In certain conditions, these ME effects are higher than those obtained with Terfenol-D/PZT composites in the same layered ring structure. Magnetostrictive and mechanical characterizations have given results that explain these high ME performances. Nevertheless, Mn-Zn ferrite/PZT composites exhibit voltages responses with low linearity especially at high signal level. Based on the particular structure of the ME device, a method to decrease the nonlinear harmonic distortion of the ME voltages is proposed. Harmonic distortion analysis of ME voltages measured in different configurations allows us to explain the phenomenon.

Effect of Sintering Temperature on Magnetic Core-Loss Properties of a NiCuZn Ferrite for High-Frequency Power Converters

In an effort to find a magnetic material for making low-loss magnetic components for high-power-density converters, we investigated the magnetic core-loss characteristics of a commercial NiCuZn ferrite (LSF 50) at 5 MHz as a function of the sintering temperature of the ferrite powder. The ferrite powder was compacted into toroid cores and then sintered at 850°C, 900°C, 950°C, 1000°C, and 1050°C for 2 h. The sintered densities of the cores increased at higher sintering temperatures. The magnetic properties of the sintered cores—complex permeability and core-loss density—were measured. We found that both the real and imaginary parts of the relative permeability increased with sintering temperature. The core-loss results at 5 MHz showed that the cores sintered at 950°C and 1000°C had the lowest core-loss densities, being two to three times lower than that of a commercial NiZn ferrite (4F1) core. Microstructures of the sintered cores were examined by scanning electron microscopy; the grains grew significantly at higher sintering temperatures.

Hydrogen production by two-step thermochemical cycles based on commercial nickel ferrite: Kinetic and structural study

One of the promising routes for hydrogen production consists of the dissociation of the water molecule through two-step thermochemical cycles based on iron oxides, i.e., ferrites. In a previous work, our group evaluated the activity of five commercial ferrites for this purpose, being Ni ferrite the one that exhibits the highest hydrogen production. In this work, the results obtained after a more exhaustive study of the thermochemical cycle based on a commercially available Ni ferrite are presented. Structural characterization of NiFe2O4 after each step of the thermochemical cycle is shown, as well as oxygen and hydrogen production over several cycles. In addition, kinetic parameters of this cycle are also studied, fitting the experimental data obtained under isothermal conditions to the most appropriate model among those ascribed to gas–solid non-catalytic multistep reaction systems.

Eddy-Current Losses in Mn-Zn Ferrites

We predict the contribution of eddy currents to power losses in polycrystalline Mn-Zn ferrites and apply it to experimental results obtained on a broad frequency range in different commercial materials and differently sized ring samples. It is verified by theory and experiment that the eddy currents can, in sufficiently large specimens, measurably contribute to the energy dissipation, in conjunction with spin damping mechanisms. In this context, the direct role of the domain wall processes is shown to be negligible, with the so-called classical losses, chiefly associated with the rotations, accounting for all of the eddy-current losses. To predict the frequency dependent classical loss W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eddy</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(cl)</sup> (f) in the actual heterogeneous material, the electromagnetic field equations are formulated under a variational multiscale approach, with fine and coarse scales identified with the thickness of grain boundary layers and grain size, respectively. The eddy-current patterns are correspondingly observed to evolve, on increasing the magnetizing frequency, from mostly grain-confined to circulating on the scale of the sample cross-section. Based on the measurement of the electrical resistivity versus frequency and knowledge of the average grain size, an overall frequency dependence of the classical loss W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eddy</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(cl)</sup> (f) is formulated. With the energy loss W(f) measured from dc to 10 MHz in different types of commercial Mn-Zn ferrites having different cross-sectional areas, it is found that the W(f) behaviors in a given material all tend to fall onto a single W(f) curve once purged of the calculated W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eddy</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(cl)</sup> (f). The residual size-independent loss is the one associated with the damping of the precessional spin motion, which can separately be accounted for.

Broadband permeability measurement method for ferrites at any magnetization state: Experimental results

This paper describes the experimental results obtained by a broadband permeability measurement method based on the full-wave electromagnetic (EM) analysis of a non-reciprocal transmission line. The method offers a new experimental tool for measuring the broadband dynamic behavior of ferrites whatever their magnetization state. The methodology and experimental setup are presented with the aim of extracting both the permittivity and the two components (diagonal μ and off-diagonal κ) of the permeability tensor. Experimental data on commercial ferrites set in different magnetization states are presented and discussed. Furthermore, this method opens perspectives for the determination of other useful magnetic parameters such as resonance linewidth ΔH. This quantity can be then measured at different frequencies, where conventional resonant methods give a value at a fixed frequency.

ESTIMATION OF THE BEHAVIORS OF SELENIUM IN THE NEAR FIELD OF REPOSITORY

The sorption of selenium ions onto iron and iron compounds as a disposal container material and its corrosion products, and onto bentonite as a buffer material, was studied to understand the behaviors of selenium in a waste repository. Selenite was sorbed onto commercial magnetite very well in solutions at around pH 9, but silicate hindered their sorption onto both magnetite and ferrite. Unlike commercial magnetite and ferrite, flesh synthesized magnetite, green rust and iron greatly decreased selenium concentration even in a silicate solution. These results might be due to the formation of precipitates, or the sorption of selenide or selenite onto an iron surface at below Eh= -0.2 V. Red-colored Se(cr) was observed on the surface of a reaction bottle containing iron powder added into a selenite solution. Silicate influences on the sorption onto magnetite and iron for selenide are the same as those for selenite. Even though bentonite adsorbed a slight amount of selenite, the sorption cannot be ignored in the waste repository since a very large quantity of bentonite is used.

Preparation and characterisation of magnetically ordered columnar structures of barium ferrite particles

In this study, we report on the columnar structures of barium ferrite particles that were prepared from water suspensions by applying a magnetic field during drying. Commercial barium ferrite (BaFe12O19) monodomain particles were used, and the surfaces of the particles were treated with an organic surfactant to reduce their agglomeration. The columnar structures were obtained by drying the water suspensions of BaFe12O19 particles on Al2O3 substrates under an applied magnetic field of 1 T. After the degradation of the organic components, the samples were sintered at 1350°C. X-ray powder diffraction, scanning electron microscopy and magnetic measurements were used to characterise the samples. When the magnetic field was applied perpendicularly to the sample plane, the as-deposited sample exhibited a higher coercivity (H c = 5434 Oe) and a higher squareness ratio (SQR = 0.76) than the sintered sample (H c = 625 Oe, SQR = 0.58). However, the sintered sample showed a higher anisotropy of the magnetic behaviour than the as-deposited sample.

High removal of phosphate from wastewater using silica sulfate

This report shows that silica sulfate is removing phosphate from wastewater very efficiently. Phosphorus removal and recovery from wastewater is a worldwide issue due to pollution of natural waters by phosphate and depletion of phosphate ores. Adsorption is a process that can remove phosphate at low concentrations. Adsorption also allows the recovery of phosphate for possible re-use. Here, we studied the adsorption of phosphate from wastewater using commercial Zr ferrite, Zr-MCM 41 and silica sulfate. We calculated equilibrium isotherms, kinetic models and thermodynamic effects under conditions similar to real wastewaters. We found that the equilibrium data for the adsorption of phosphate were best fitted to the Freundlich model. The results show that the maximum uptake of phosphate was 3.36 mg g−1 for Zr-MCM, 27.73 mg g−1 for Zr ferrite and 46.32 mg g−1 for silica sulfate. The kinetic results of the three adsorbents were satisfactorily predicted using a pseudo-second-order model. We found that silica sulfate provided excellent characteristics in terms of the maximum adsorption and rate constant for the adsorption of phosphate. The thermodynamic data showed that increasing the temperature enhanced the adsorption of phosphate onto silica sulfate. Our findings will help to define efficient methods to remove phosphate from wastewater.

Comparative study of the activity of nickel ferrites for solar hydrogen production by two-step thermochemical cycles

In this work, we compare the activity of unsupported and monoclinic zirconia – supported nickel ferrites, calcined at two different temperatures, for solar hydrogen production by two-step water-splitting thermochemical cycles at low thermal reduction temperature. Commercial nickel ferrite, both as-received and calcined in the laboratory, as well as laboratory made supported NiFe 2O 4, are employed for this purpose. The samples leading to higher hydrogen yields, averaged over three cycles, are those calcined at 700 °C in each group (supported and unsupported) of materials. The comparison of the two groups shows that higher chemical yields are obtained with the supported ferrites due to better utilisation of the active material. Therefore, the highest activity is obtained with ZrO 2-supported NiFe 2O 4 calcined at 700 °C.

Comparison of Losses Measurement in a Ferrite With Two Calorimetric Methods

Most of the papers in the literature dealing with magnetic losses present results obtained with flux metric methods. But those techniques of measurement are known to be inaccurate when the voltage and current probes of the device introduce a significant phase shift at high frequencies. As a consequence, it is important to develop alternative methods to measure losses in magnetic materials. A natural way of measurement is the calorimetric method which is by principle free of the above mentioned problem. Here, we propose to compare results obtained with two different calorimetric methods. Experiments were conducted on a commercial Mn-Zn ferrite under sinusoidal waveform induction for frequencies varying from 10 kHz to 200 kHz. The two methods give close results and some explanations for the differences are provided.