Mn-Zn Ferrite Research Articles

Influence of MnZn Ferrite Homogeneous Fibers on the Microstructure, Magnetic, and Mechanical Properties of MnZn Ferrite Materials

MnZn ferrite homogeneous fibers were synthesized via a simple solvothermal method and they were used as a reinforcing phase to prepare homogeneous-fiber-reinforced MnZn ferrite materials. The effects of MnZn ferrite homogeneous fibers (0 wt% to 4 wt%) doping on the microstructure, magnetic, and mechanical properties of MnZn ferrite materials were studied systematically. The results showed that MnZn ferrite homogeneous fibers exhibited high purity, good crystallinity, and smooth 1D fibrous structures, which were homogeneous with MnZn ferrite materials. Simultaneously, a certain content of MnZn ferrite homogeneous fibers helped MnZn ferrite materials exhibit more uniform and compact crystal structures, less porosity, and fewer grain boundaries. In addition, the homogeneous-fiber-reinforced MnZn ferrite materials possessed superior magnetic and mechanical properties such as higher effective permeability, lower magnetic loss, and higher Vickers hardness compared to ordinary MnZn ferrite materials. In addition, the magnetic and mechanical properties of homogeneous-fiber-reinforced MnZn ferrite materials first increased and then gradually decreased as the homogeneous fiber content increased from 0 wt% to 4 wt%. The best magnetic and mechanical properties of materials were obtained as the fiber content was about 2 wt%.

Correlating the microstructure of Mn–Zn ferrite with magnetic noise for magnetic shield applications

Many sensitive atomic devices require magnetic shield to reduce external magnetic field interference. Mn–Zn ferrites are optimistic candidates for shielding because they provide a high shielding factor and a low magnetic noise. This study evaluated the magnetic noise of Mn–Zn ferrite magnetic shield based on its grain size. The morphologies of Mn–Zn ferrite samples were characterized to establish a correlation between their grain sizes and magnetic permeability, which can be used to calculate magnetic noises. The correlation was then used to evaluate the shielding performance of another Mn–Zn ferrite, where the magnetic noise of the magnetic shield made from the ferrite was calculated to be 2.53 f−1/2fT. The magnetic noise of the magnetic shield was also measured experimentally using a spin-exchange relaxation-free atomic magnetometer. The measured magnetic noise of ferrite shield was 2.61 f−1/2fT, while the white noise of the atomic magnetometer was 0.71 fT/Hz1/2 below 100 Hz. The consistency between the experimental results and predicted values suggests the viability of the proposed approach, providing a convenient, efficient, and precise method for developing ferrite ceramics materials for low-noise magnetic shields.

Measurement Methods for High-Frequency Characterizations of Permeability, Permittivity, and Core Loss of Mn-Zn Ferrite Cores

Manganese–zinc (Mn-Zn) ferrites are the primary choice for high-frequency and high-power magnetic components. Optimum material selection is essential for high-performance magnetic component design. However, the manufacturers’ material specifications usually do not provide sufficient information to optimize the design. Complex permeability and permittivity, as well as specific power loss, are typically provided as one value, regardless of the core shape and size. Magnetic component design based on these incomplete specifications can result in a poorly optimized component. This article proposes methods to determine the properties of Mn-Zn ferrite at high frequencies, with tests up to 20 MHz. This article also presents experimental complex permeability and permittivity frequency characteristics for four ferrite materials: 3E10, 3F36, 3E65, and 3C95. The resulting fitted parameters for the equivalent-circuit model can be used in any design algorithm or simulation tool. The impacts of physical size, temperature and force on complex permeability and permittivity are also considered.

Ferrite materials with high saturation magnetic induction intensity and high permeability for magnetic field energy harvesting: Magnetization mechanism and Brillouin function temperature characteristics

Manganese-zinc (MnZn) ferrites play an indispensable role in energy transform and harvesting. It is notable to mention that the combined enhancement of initial permeability (μi), saturation magnetic induction (Bs) and Curie temperature (Tc) is conducive to improving the output power and safety of magnetic field energy harvesting devices. In this paper, high permeability MnZn ferrites were synthesized by a conventional oxide ceramic method. The thermomagnetic curves of MnZn ferrites were fitted according to the Néel molecular field theory (NMFT) and the Brillouin function. Then the molecular field coefficient γaa, γab, γbb, and Tc were calculated. Aiming at the magnetization mechanism of permeability, the contributions of domain wall motion and spin rotation were analyzed by fitting the complex permeability spectrum. Furthermore, the temperature characteristics of μi and Bs are analyzed, and we simulated and compared the effect of different magnetic properties of MnZn ferrites on the output of non-invasive magnetic field harvester. The MnZn ferrites with superior comprehensive performance own potential applications for non-invasive magnetic field harvester.

Modern Advances in Magnetic Materials of Wireless Power Transfer Systems: A Review and New Perspectives.

The magnetic coupling resonant wireless power transfer (MCR-WPT) system is considered to be the most promising wireless power transfer (WPT) method because of its considerable transmission power, high transmission efficiency, and acceptable transmission distance. For achieving magnetic concentration, magnetic cores made of magnetic materials are usually added to MCR-WPT systems to enhance the coupling performance. However, with the rapid progress of WPT technology, the traditional magnetic materials gradually become the bottleneck that restricts the system power density enhancement. In order to meet the electromagnetic characteristics requirements of WPT systems, high-performance Mn-Zn and Ni-Zn ferrites, amorphous, nanocrystalline, and metamaterials have been developed rapidly in recent years. This paper introduces an extensive review of the magnetic materials of WPT systems, concluding with the state-of-the-art WPT technology and the development and application of high-performance magnetic materials. In addition, this study offers an exclusive reference to researchers and engineers who are interested in learning about the technology and highlights critical issues to be addressed. Finally, the potential challenges and opportunities of WPT magnetic materials are presented, and the future development directions of the technology are foreseen and discussed.

A systematic investigations on effect of annealing temperature on magnetic properties of a promising soft magnetic Co35Cr5Fe10Ni30Ti20 HEA

The present study investigates the effect of different annealing temperatures on phase formation, microstructure, and their correlation with magnetic properties of a promising soft magnetic Co35Cr5Fe10Ni30Ti20 High Entropy Alloy (HEA) design developed by our research group previously. We reproduced the Co35Cr5Fe10Ni30Ti20 HEA through the mechanical alloying and found the mixture of fcc and R-phase having Ms = 74.8 emu/g and Hc= 12.92 Oe. The different annealing temperature was decided based on the DTA analysis of the synthesized sample. The samples were annealed at 200, 500, 700, 790, 870, and 965 ͦ C for 2 h to study the change in the phase evolution and magnetic behavior. Phase transformation was observed for 500 ͦ C annealed HEA, and the value of Ms (82.38 emu/g) and Hc (41.49 Oe) increased after annealing at 500 ͦC. Interestingly, the samples annealed at high temperatures (>700 °C) have a high value of Ms and a significantly low value of Hc (<2 Oe). Among annealed Co35Cr5Fe10Ni30Ti20 HEA, 790 ͦ C annealed HEA has the highest value of Ms (90.79 emu/g) and the lowest Hc (1.66 Oe)of HEAs reported so far. The concluding reason behind the high value of Msfor annealed HEAs area decrease in lattice parameter, i.e., improved magnetic interaction and a change in volume phase fraction of synthesized phases. However, the soft magnetic behavior of high-temperature annealed HEA is attributed to the synergetic effect of the decrease in magneto-crystalline anisotropy, particle size, and surface anisotropy. The value of Ms and Hc for the 790 ̊C annealed HEA is comparable to some commercial soft magnets, such as Supermalloy, Ni-Zn ferrite, and Mn-Zn ferrite. Thus, the designed and developed Co35Cr5Fe10Ni30Ti20HEA showed excellent soft magnetic characteristics even after annealing at high temperatures and may be further considered for industrial applications.

Sm3+ doped Mn-Zn mixed ferrites: Synthesis and characterization

Pure and Samarium (Sm3+) doped Mn-Zn ferrites were synthesized using Co-precipitation method. The Sm3+ concentration varied from 0.1% to 0.3%. This was added to the solution during the synthesis of Mn-Zn ferrites (Mn0.5Zn0.5Fe2O4) at room temperature. The precipitate so obtained was annealed at 200℃ for 4 h and then crushed to powder. The powdered material was subjected to structural, morphological, compositional, optical and magnetic characterization. XRD shows cubic spinal structure with crystallite size of the order of 6 nm. TEM and SEM images show spherical particles are in good agreement with XRD data. EDAX indicates stoichiometry of elements present in material. FTIR shows various functional groups and doped samarium. VSM for pure Mn:Zn ferrite show hysteresis with high magnetization, coercivity and low remanence. All the magnetic parameters decrease on 0.1% Sm3+ doping. These parameters get increased, compared to values at 0.1% doping, on increasing Sm3+ doping to 0.2%. On further increasing Sm3+ doping to 0.3%, the magnetic parameters show insignificant changes. VSM shows that Sm3+ affects magnetic properties significantly only at lower doping concentrations. These changes are due to Sm3+ substitution at tetrahedral and octahedral positions. The ionic radii mismatch in between Samarium and iron influence the magnetic parameters of Mn0.5Zn0.5Fe2O4.

A High-Performance Magnetic Shield with MnZn Ferrite and Mu-Metal Film Combination for Atomic Sensors.

This study proposes a high-performance magnetic shielding structure composed of MnZn ferrite and mu-metal film. The use of the mu-metal film with a high magnetic permeability restrains the decrease in the magnetic shielding coefficient caused by the magnetic leakage between the gap of magnetic annuli. The 0.1–0.5 mm thickness of mu-metal film prevents the increase of magnetic noise of composite structure. The finite element simulation results show that the magnetic shielding coefficient and magnetic noise are almost unchanged with the increase in the gap width. Compared with conventional ferrite magnetic shields with multiple annuli structures under the gap width of 0.5 mm, the radial shielding coefficient increases by 13.2%, and the magnetic noise decreases by 21%. The axial shielding coefficient increases by 22.3 times. Experiments verify the simulation results of the shielding coefficient of the combined magnetic shield. The shielding coefficient of the combined magnetic shield is 16.5%. It is 91.3% higher than the conventional ferrite magnetic shield. The main difference is observed between the actual and simulated relative permeability of mu-metal films. The combined magnetic shielding proposed in this study is of great significance to further promote the performance of atomic sensors sensitive to magnetic field.

Tailoring the refractive index of impedance-matched ferrite composites

Independent control of the magnetic and electric properties of two-part and three-part ferrite composites is demonstrated through variation of particle size and volume fraction of ferrite inclusions. This provides a route to creating broadband impedance-matched composites with tailored high refractive-index values. A two-part composite comprising NiZn ferrite in a PTFE dielectric host with approximately equal values of relative real permittivity and permeability up to 100 MHz is manufactured. The refractive index for NiZn–PTFE composites, measured at 20 MHz, is 6.1 for NiZn volume fraction of 50%vol. and 6.9 for NiZn volume fraction of 70%vol. Similarly, we have characterised a three-part composite with a refractive index of approximately 16 up to 60 MHz. The three-part composite comprises NiZn and MnZn ferrites in a PTFE dielectric host matrix with a percentage volume ratio of 65%: 15%: 20%, respectively.

Effect of a YIG nanoparticle additive on the magnetic properties of MnZn ferrites for MHz frequency applications

AbstractIn this study, MnZn ferrites with added YIG nanoparticles were developed for MHz frequency applications. The effect of the magnetic YIG additive on the power loss, initial permeability, and cutoff frequency of MnZn ferrites was investigated. A small quantity of added YIG effectively reduces the power loss and concurrently increases the initial permeability. Compared to the results for the MnZn ferrite with no added YIG, the optimal MnZn ferrite with 600 ppm added YIG exhibits a reduction in the power loss at 25°C of 56.4% and 36.6% at 1 MHz/50 mT and 3 MHz/10 mT, respectively, and a 13.9% increase in the initial permeability. This sample also exhibits a good stability of the power loss against temperature. The power loss remains below 205 kW/m3 over temperatures ranging from 25 to 140°C. The effect mechanism of YIG addition on the magnetic properties of MnZn ferrites was studied. An analysis based on the equivalent circuit model showed that the reduction in the eddy current loss and power loss mainly results from the increase in the grain boundary resistance caused by the addition of highly resistive YIG.

Effect of Ni substitution and annealing temperature on structural and magnetic properties of MnZn-Ferrites: Cytotoxicity study of ZnO and SiO2 coated core shell structures

Magnetic spinel ferrite nanoparticles (NPs) have a broad scope of applications based on their structural properties, including in lithium-ion batteries, catalysts, electrochemical energy storage, drug delivery, magnetic hyperthermia, and photothermia. In this study, we investigated the structure, crystallographic phase formations, and magnetic properties of Ni-substituted MnZn ferrites (MZFs), Mn(0.6-x)Zn(0.4-y)Ni(x+y)Fe2O4 (x = 0–0.6, y = 0; y = 0–0.4, x = 0) compositions of as-prepared (AP) and air annealed (350–1200 °C) samples. All AP NPs exhibited a pure spinel structure. Ni-MZF compositions annealed at 600 °C had high α-Fe2O3 secondary phase content in Ni-MZFs (Ni substituted for Zn), whereas Ni-MZFs with x = 0.4 (Ni substituted for Mn) had no impurities, and its magnetization (50 emu/g) was enhanced compared with that of the other samples. X-ray photoelectron spectroscopy revealed that Fe3+ cations were present in tetrahedral and octahedral sites. The single spinel phase reappeared with improved crystallinity in all Ni-MZFs by annealing at 1200 °C and exhibited superior magnetization (60–73 emu/g) compared with that of MZF (35 emu/g). Additionally, the spinel phase was stabilized in the ZnO- and SiO2-coated Ni-MZF core shell structures annealed at 700 °C with higher magnetization than MZF. Moreover, Ni-MZF core shell structures exhibited biocompatibility and may have biomedical applications.

Low power loss manganese ferrites with the addition of Ta2O5 for MHz applications

Dramatic increase of power loss in the MHz frequency range is the bottleneck problem for MnZn ferrites to be applied in high-frequency power electronic devices. In this work, manganese ferrites with low power loss in the frequency range of 1–3 MHz have been developed by the addition of Ta2O5. The manganese ferrite with 300 ppm Ta2O5 exhibits excellent Pcv performance. Pcv at 25 °C is as low as 41, 94 and 164 kW/m3 under measurement conditions of 1 MHz/50 mT, 2 MHz/50 mT and 3 MHz/30 mT, respectively. Excellent temperature stability of power loss in the temperature range of 25–140 °C is also achieved in this sample. Power loss was divided to three parts of hysteresis loss, eddy current loss and residual loss. Ta2O5 segregates at grain boundaries and reduces all three parts of loss. The mechanism of Ta2O5 influence on each part of loss has been clarified.

Synthesis, Electron Spin Resonance and Photoluminescence properties of Sm3+ ion doped Zn-Mn nanoferrites synthesized by glycol-thermal method

Nanocrystalline Zn0.5Mn0.5SmxFe2-xO4 (0 ≤ x ≤ 0.05) with average crystallite sizes varying between 12 and 17 nm were synthesized by the glycol-thermal process. X-ray diffraction (XRD) analysis confirmed a single-phase cubic spinel structure in all the compounds. Substituting a smaller Fe3+ ion with a larger rare-earth (RE) Sm3+ ion has affected the distribution of metal ions on tetrahedral (A) and octahedral (B) sites. In this work, a comprehensive study has been carried out on nanocrystalline particles of RE Sm3+ ion doped into Zn-Mn ferrite to estimate intrinsic strain through Williamson-Hall (W–H) analysis. The results were compared with those obtained from the Debye Scherrer equation. Tensile microstrain within the nanocrystals were detected from W-H plots for x = 0, 0.01,0.02 and 0,05 samples, while compressive microstrain was observed for x = 0.02 and 0.05 samples. A scanning electron microscope (SEM) has been used to study the morphology of nanoparticles and it revealed spherical-shaped nanoparticles. Energy dispersive X-rays (EDX) confirmed the phase purity and the elemental composition with no impurity elements were observed. Crystallite sizes affect electron spin resonance (ESR) signal intensity and the line width. The g-values fluctuated ranging from 2.31 to 2.51 due to fluctuating crystallite sizes. Photoluminescence (PL) displayed a blue-violet emission with maxima centred at 418 nm and 438 nm under the excitation wavelength of 320 nm. The electron spin resonance and photoluminescence results show that the Sm doped Zn-Mn ferrites are promising candidates for applications in blue LEDs.

Investigation of Magnetic and Photocatalytic Properties of CoFe2O4 Doped La3+, Nd3+, I3+

Cobalt ferrites are widely used for permanent magnets, magnetic fluids, microwave devices, high density information storage and environmental technologies. The properties of nanosized magnetic materials strongly depend on the shape, size, and phase composition of the particles. The great interest of researchers in nanosized materials in recent years is associated with the possibility of changing the properties of magnetic materials by controlling the particle size and distribution of cations over sublattices in ferrite [1].Nanoparticles of doped cobalt ferrite showed improved physicochemical characteristics compared to individual components due to the synergistic effect of the mutual presence of cations. Currently, various technologies for producing ferrites are used. However, to obtain a single-phase product, calcination of the precursors at a temperature of 1300-1500 0C is required, which causes agglomeration and sintering of the product. The use of modern methods of electrochemical synthesis is the basis for obtaining ferrites from transition materials with a given set of properties. A characteristic recent trend is the development of new technologies and compositions for the production of precisely nanodispersed ferrites [2].The purpose of this work is to study the possibility of using contact low-temperature nonequilibrium plasma for the synthesis of cobalt ferrites doped with La3+, Nd3+, I3+ cations, to establish a relationship between the cationic composition of ferrites and its phase composition, magnetic and structural characteristics.Ferrites were synthesized in the form of nanoparticles using contact nonequilibrium low temperature plasma in an electrochemical reactor. The crystalline microstructure of the samples was revealed by X-ray diffraction and X-ray phase methods. The magnetic characteristics were determined from hysteresis loops. The EPR spectra were obtained on a Radiopan SE/X-2543 radiospectrometer. To characterize the EPR signals, the intensity and width of the signal, and the resonant frequency were used. The visualization of the dependences of the technological characteristics of La3+-Nd3+-I3+ ferrites on the cationic composition was carried out by the simplex method using the STATISTICA 12 program.It has been established that the nature of the rare-earth metal cation in cobalt ferrite directly determines the magnetic and photocatalytic properties of spinel ferrites. The effect of the mutual influence of the content of cations on the saturation magnetization and coercive force is determined. The most influencing factor is the content of neodymium cations. Low values of the coercive force for Mn-Zn and Co-Zn ferrites and high values for the entire range of Co-Mn ferrites are established. An increase in the content of cobalt cations leads to an increase in the saturation magnetization value of Co-Mn ferrites. The EPR spectra show that the values of the resonance field and linewidth in the EPR spectrum correlate with the value of magnetic saturation.Simultaneous substitution of Nd3+ and La3+ in CoFe2O4 nanoparticles affected the structure, magnetic and photocatalytic properties. Structural parameters were investigated and calculated using X-ray diffraction studies. The magnetization analyzes were carried out at room temperature. Various magnetic parameters have been obtained and discussed, including remanence (Mr), coercive force (Hc), saturation magnetization (Ms), squareness ratio (SQR=Mr/Ms) and magnetic moment (nB). An increase in Mr, Ms, Hc and nB was found at lower concentrations of Nd3+ and La3+. An increase in the content of Nd3+ cations leads to a significant increase in the coercive force. The analysis of photocatalytic activity in the reaction of isolation of furacilin showed the best results (destruction rate 98%, time 40 minutes) for the ternary composition.References Caldeira, Luis Eduardo, et al. "Correlation of synthesis parameters to the structural and magnetic properties of spinel cobalt ferrites (CoFe2O4)–an experimental and statistical study." Journal of Magnetism and Magnetic Materials550 (2022): 169128.Lu, Yuzheng, et al. "Effect of Gd and Co contents on the microstructural, magneto-optical and electrical characteristics of cobalt ferrite (CoFe2O4) nanoparticles." Ceramics International2 (2022): 2782-2792.

Electromagnetic (EM) wave absorption properties of cementitious building composites containing MnZn ferrite: Preferable effective bandwidth and thickness via iron and graphite addition

Long-term EM radiation seriously affects human physical and mental health. MnZn ferrite can improve the microwave absorbing property of cementitious composites, while obvious shortcomings are narrow effective bandwidth and large thickness. In this work, the intensified effects of metallic iron and graphite powders addition on the magnetic properties, impedance matching, EM wave attenuation, and reflection loss (RL) of cementitious composites containing MnZn ferrite were investigated by VSM and VNA. The phase composition, microstructure, and hydration of the composites were analysed by XRD, XPS, SEM–EDS, and FTIR analyses to explore the relationship between the physicochemical properties and EM properties. The favorable EM wave absorption of composites lies in the magnetic loss and dielectric loss with the addition of iron and graphite powder. MnZn ferrite and iron powder addition can effectively improve the dissipation of electric energy and magnetic energy, and reduce the “superior” thickness range (STR) of the composites. 3% iron powder addition can decrease the STR from over 17.3 mm to 9.4–16.3 mm. Taking the thickness of 11.5 mm as an example, the minimum RL and the mean RL of the composite were reduced by 101.3% and 13.2%, respectively, while the effective bandwidth (RL < − 10 dB) was increased from 1.78 GHz to 2.61 GHz. 3% graphite addition decreased the minimum RL of the composite containing both MnZn ferrite and iron powder from −35.3 dB to −43.9 dB at a thickness of 11.5 mm. Meanwhile, the mechanical strength of cementitious composites is sufficient to satisfy the requirements in most building applications.

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.

Aqua Cobalt Ferrite/Mn–Zn Ferrite Hybrid Nanofluid Flow Over a Nonlinearly Stretching Permeable Sheet in a Porous Medium

In the present article, the problem of ferro hybrid nanofluid flow over a nonlinearly stretching permeable sheet in a porous medium has been studied. The main motivation of this research is to present a comprehensive analysis of the hydrodynamics and thermal boundary layers as well as the skin friction and heat transfer as two important quantities of engineering interest for the relevant ferro hybrid nanofluid flow. The ferro hybrid nanofluid is a nanofluid that can be composed of several nanoparticles and has a magnetic property; it means that has its own behavior in the magnetic field. Two different types of ferroparticles, namely, Mn–Zn ferrite (Mn–ZnFe2O4) and cobalt ferrite (CoFe2O4) are considered with water as a base fluid. The similarity solution is used to decrease the governing set of partial differential equations (PDEs) to the nonlinear ordinary differential equations (ODEs) system, which is solved numerically by the bvp4c function of MATLAB. The effects of pertinent parameters, namely, magnetic parameter, nonlinear velocity parameter, permeability parameter, and volume fraction of the second nanoparticle on velocity and temperature profiles, skin friction coefficient, and local Nusselt number are computed and shown through graphs. The prominent novelty of this research is related to the use of ferro hybrid nanofluid as a working fluid, where many studies have been carried out in the field of the determination of heat transfer and skin friction in nanofluids/ferro nanofluids on different geometries. To the best of our knowledge, no one has ever attempted to study the present boundary layer problem with applying ferro hybrid nanofluid. The results of this paper indicate that Nusselt number and skin friction coefficient decrease with increasing magnetic field.

Co-precipitation method for the preparation of Mn-Zn Ferrite and study their Structural and Magnetic properties

"Ferrite nanoparticles were synthesized using the co-deposition method with pH = 12. This paper discusses the differences in composition and magnetic properties that contribute to the MnZn ferritic's properties. Samples were prepared, fabricated and annealed at two temperatures (600°C, 900°C). The crystal structure of the prepared samples was obtained using X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy (FTIR) and field emitting electron microscopy (FESEM), respectively. The magnetic properties of the samples prepared by assay (VSM) were obtained and the magnetic and structural properties were discussed based on the changing temperature."

Effect of compressive stress on power loss of Mn–Zn ferrite for high-frequency applications

In this work, the low-power-loss Mn–Zn ferrite was prepared by the traditional ceramic sintering process. This sample shows the good wide-temperature stability of power loss (Pcv). In the whole measurement temperature range of 25 - 120 °C, Pcvs maintain less than 100, 682, and 1455 kW/m3 at 100 kHz/100 mT, 500 kHz/100 mT and 800 kHz/100 mT, respectively. The effect of uniaxial compressive stress on power loss at 100, 500 and 800 kHz was investigated. Stress has greater impact on Pcv at high frequencies and Pcv increases remarkably. To clarify the mechanism of stress on power loss, Pcv was divided into three parts including hysteresis loss (Phv), eddy current loss (Pev) and residual loss (Prv), and the effect of stress on each part of loss was discussed. At the low frequency of 100 kHz, Pcv is mainly contributed by Phv. The applied stress leads the local anisotropic stress and makes domain wall displacement more difficult, which is the reason of the increase of Phv. When frequency increases to 500 and 800 kHz, Pev and Prv become more important. The compressive stress is in favour of electron transfer between Fe3+ and Fe2+ in grains and electron tunnelling effect at grain boundaries, which leads to the decrease of resistivity. This is the origin of enhanced Pev under the compressive stress. The enhanced Prv is related to the enhanced electronic diffusion under the compressive stress. The clarification of the mechanism of stress on power loss is beneficial to develop new soft ferrite materials with low stress sensitivity for high-frequency applications.

Titanium Oxide Coatings Deposited on MnZn Ferrite by a Molten Salt Reaction

Using molten salt reactions, Ti oxide coatings were successfully deposited on MnZn ferrite in a NaCl–KCl–K2TiF6 melt. The film formed on the surface of MnZn ferrite had a thickness of up to 20 μm and was composed of Ti oxides. The electric conductivity of the coatings was contributed to by the component Ti2O3 and depended on the concentration of Ti2O3 in the film. When the Ti2O3 content in the film increased, the surface resistance dropped to the order of 10−1 Ω/□. The conductive film had the potential to be welded to the metal electrode, thus confirming that the molten salt reaction method could be used as a pre-treatment to realize the metallization of MnZn ferrite.