A review on MnZn ferrites: Synthesis,characterization and applications

Researchers are taking great interest in the synthesis and characterization of MnZn ferrites due to their wide range of applications in many areas. MnZn ferrites are a class of soft magnetic materials that have very good electrical, magnetic and optical properties. The properties of MnZn ferrites include high value of resistivity, permeability, permittivity, saturation magnetization, low power losses and coercivity. The above mentioned advantageous features of MnZn ferrites make them suitable for the use in various applications. In biomedical field these ferrites are used for cancer treatment and MRI. MnZn ferrites are also used in electronic applications for making transformers, transducers and inductors. These ferrites are also used in magnetic fluids, sensors and biosensors. MnZn ferrite is highly useful material for several electrical and electronic applications. It finds applications in almost every household appliances like mobile charger, LED bulb, TV, refrigerator, juicer mixer, washing machine, iron, microwave oven, mobile, laptop, desktop, printer and so on. Therefore, the present review focuses on different techniques for synthesis of MnZn ferrites in literature, their characterization tools, effect of doping on the properties of MnZn ferrite and finally we will discuss about their applications.     

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

In 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.     

Two-step doping of SiO2 and CaO for high-frequency MnZn power ferrites

SiO₂ and CaO are empirical but effective co-doping oxides for low-loss MnZn soft ferrites. However, the underlying mechanism of the synergistic effect remains unclear. Herein, we systematically investigate the effect of SiO₂ and CaO, and propose a two-step doping strategy for high-frequency MnZn ferrites. It is found that SiO₂ facilitates the formation of mono-domain grains, thereby reducing the residual loss at high frequency. Meantime, CaO may dissolve into ferrite matrix with improved resistivity but abnormal growth of grains. By preliminarily coating MnZn particles with SiO₂, the reaction between CaO and ferrite matrix could be effectively suppressed, leading to the formation of continuous calcium silicate grain boundary (GB) phase. Consequently, superior high-frequency performance than traditional one-step doping strategy including initial permeability of 498, cut-off frequency of 12.6 MHz, power loss of 326 kW/m³ (5 MHz, 10 mT) can be obtained, which is desired by miniaturized electronic devices.     

Correlating the microstructure with magnetic properties of Ti-doped high-frequency MnZn ferrite

In this study, high-frequency MnZn ferrites are prepared for power applications at 10 MHz using solid-state reaction method. The sample doped with 3000 ppm TiO₂ yields the optimal comprehensive magnetic properties, with an initial permeability of 792, power loss of 415 kW/m³ (10 MHz, 5 mT, 25 ℃), and saturation induction of 460 mT. This indicates significant progress compared to previously reported results. The mechanisms of property optimisation, microstructure and domain structure evolution also discussed with TiO₂ doping. The precipitation of Ti at the grain boundary can promote a high-density microstructure and favour the formation of magnetic monodomain in MnZn ferrites. Our results elucidate the correlations between microstructure, domain structure, and high-frequency performance, and present a potential roadmap for the development of high-frequency soft magnetic ferrites.     

Influence of the Addition of Bi2O3 on the Grain Growth and Magnetic Permeability of MnZn Ferrites

Additions of Bi₂O₃ were used to promote grain growth and to increase magnetic permeability during sintering of MnZn ferrites. The results showed that small additions of Bi₂O₃ of <0.05 wt% remarkably increase the permeability of MnZn ferrites. On the other hand, addition of 0.05 wt% Bi₂O₃ induced the formation of a microstructure composed of giant grains with trapped pores embedded in a normal microstructure. The permeability of these samples showed a pronounced secondary maximum in permeability. At still higher Bi₂O₃ concentrations, above 0.2 wt%, the grain growth was retarded and a normal microstructure appeared; however, the magnetic permeability was strongly reduced.     

Preparations,optical, structural,conductive and magnetic evaluations of RE's (Pr,Y, Gd,Ho, Yb) doped spinel nanoferrites

Rare earths RE's (Pr, Y, Gd, Ho, Yb) substituted MnZn spinel ferrites with composition of Mn_0.5Zn_0.5M_0.02Fe_1.98O₄ (M = Pr, Y, Gd, Ho, Yb) are prepared by sol gel combustion approach. Low sintering temperature (500 °C) is used to sinter the RE's doped MnZn samples. MnZn samples are further characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) to measure the cubic crystalline structure, particle size, morphology, porosity and grain size. Cubic crystalline phase of prepared RE's doped MnZn ferrites is confirmed by x-ray diffraction (XRD). The morphology, porosity and grain size are observed using FESEM. The magnetic properties of RE's doped MnZn nanoferrites are analyzed by vibrating sample magnetometer (VSM). Coercivity (H_c), remanence (M_r) and saturation magnetization (M_s) are calculated from the magnetic loops. The saturation and remanence of the nanoferrites are increased by the substitution of RE's metal ions and varies from 14.76 to 26.36 emu/g and 9.98–22.48 emu/g respectively. Bohr magneton and anisotropy constant are calculated from the recorded magnetic data. The conductive analysis of the prepared samples is studied at 40 °C −300 °C temperature, leading to the conductivity measurements from 1.12 × 10^-2 Ω^-1-cm^-1 to 9.52 × 10^-2 Ω^-1-cm^-1. UV–Vis spectroscopy is used to determine the semi conducting nature of RE's doped MnZn spinel ferrite samples. The magnetic, conductive and optical study of the RE's doped MnZn nanoferrites sintered at low temperature suggests the use of these materials for microwave absorption, supercapacitor, lithium ion batteries and nanoelectronics industrial applications.     

掺杂对共沉淀法制备的锰锌铁氧体性能的影响

通过加入添加剂,制备了晶相单一、结晶度完好、具有较好磁性能的锰锌铁氧体纳米晶,然后研究添加剂对铁氧体晶相、磁性能和居里温度的影响.研究结果表明:添加剂可以使晶体生长更完善,晶粒变大;同时可以改善样品的磁性能,降低居里温度.     

Geometry and Electrical Properties of Grain Boundaries in Manganese Zinc Ferrite Ceramics

For large-grained manganese zinc (MnZn) ferrite ceramics, grain misorientation determined by electron backscatter diffractions and grain-boundary resistance measured using microcontact impedance spectroscopy have been correlated. The degree of oxidation of grain boundaries and, hence, the barrier height depends on the overall grain-boundary network as well as on the individual boundary structure; therefore, a statistical analysis has been performed based on several hundreds of local measurements. When the boundaries are divided into low- and high-resistance groups, statistically significant differences in rotation axis and angle distributions are found. The misorientation distribution of the low-resistance boundary group is suggested to reflect the low-energy configurations of boundary planes in MnZn ferrites.     

The effects of Barium Strontium Titanate (BST) on the soft magnetic properties and loss performance of MnZn ferrites

With the increasing power density of the switched mode power supply (SMPS) developed nowadays, higher efficiency is required from the magnetic core, where the MnZn ferrites are often adopted. However, the relatively high operating temperature of the SMPS often results in reduced resistivity of the MnZn, which increases the eddy current loss. To enhance the resistivity of MnZn ferrite at high temperature range (>100 °C), donor-doped barium strontium titanate (BST) with a positive temperature coefficient of resistivity (PTCR) is prepared and dopped in the MnZn ferrite. The influence of BST addition from 0.000 wt% to 0.020 wt% on the MnZn ferrite is investigated over a wide temperature range from 25 °C to 140 °C. The XRD result suggests ionic exchange between the spinel phase and perovskite phase. The SEM result shows a refined and more uniform microstructure of MnZn ferrite brought about by the BST addition. At the maximum of 0.020 wt%, the BST addition shows almost no influence on density and the saturation magnetic induction. However, the initial permeability is slightly reduced by the BST addition, due to the microstructural change. Moreover, the BST concentrating at the grain boundaries improves the DC-resistivity across the temperature range from 25 °C to 140 °C. Due to the addition of BST, the reduction in eddy current loss at 300kHz/100 mT is around 35% at 25 °C, and ∼20% reduction at 140 °C.     

Nonstoichiometry and Its Effect on the Magnetic Properties of a Manganese-Zinc Ferrite

The effect of oxygen nonstoichometry on physical and magnetic properties of a Mn-Zn ferrite has been studied by using annealed samples under various oxygen pressures and temperaure. The dependence of oxygen nonstoichiometry7 on disaccommodation and Fe²⁺ content changed at the stoichiometric composition, and the lattice parameter became maximum at the stoichiometric composition. These results suggest that Mn-Zn ferrites have two different defect structures: cation vacancies in cation-deficient regons and oxygen vacancies in anion-deficient regions. Initial permeability was maximum and power loss was minimum at the stoichiometric composition, suggesting he importance of the number of point defects for the magnetic properties.     

Engineering High Permeability: Mn–Zn and Ni–Zn Ferrites

Magnetic properties of polycrystalline spinel ferrites are of significant interest in scientific community. Of all, initial permeability is most important magnetic property for device fabrication. Mn–Zn and Ni–Zn ferrites are commercially most successful class of ferrites. Ferrites accommodate variety of cations in interstitial sites; type of cations, their occupancy at interstitial sites, grain size, pores, defects, or other imperfections in ferrites regulate their response to external magnetic stimulus. These factors are influenced by composition and preparation method. The failure of initial permeability of ferrites, to withstand variation in frequency of applied signal has fueled intense efforts in scientific community to optimize frequency stability of permeability. Therefore, improvement in their permeability is important from commercial perspective, and it further enables deeper insight into the dynamical link between microstructure and magnetic properties. This work presents a review of initial permeability in Mn–Zn and Ni–Zn ferrites with a focus on influence of intrinsic factors and frequency of applied signal. The work is an analytical assessment to provide framework for engineering high permeability in ferrites.     

Nickel-zinc ferrites with additives for use in magnetic heads

The effect of the addition of Na₂O, CaO and ZrO₂ on the properties of NiZn ferrite, manufactured by the classical method, was studied. Because the porosity, resistivity, permeability and saturation magnetisation are affected, it is possible to select the kind of additive needed to produce NiZn ferrites with electrical and magnetic properties suitable for magnetic heads.     

铜电炉冶炼贫化渣焙烧富集Fe3O4

以云南某铜冶炼厂电炉贫化渣为原料,在有氧气氛下加入CaO高温焙烧铜渣,分析了焙烧时间、焙烧温度、铜渣粒度、气相气氛对磁化焙烧效果的影响,利用SEM和XRD等对焙烧样品的微观形貌、物相变化进行分析,并通过热重分析考察了添加CaO及研磨粒度对铜渣焙烧过程的影响. 结果表明,加入CaO能有效促进Fe2SiO4分解,磨矿越细越有利于反应进行,随焙烧温度提高、焙烧时间延长,a-Fe2O3增多,而Fe3O4先增加、温度超过850℃后减少;过高温度及过长焙烧时间不利于Fe3O4富集,且过低的氧势不利于富集Fe3O4的气固反应进行,Fe3O4富集的优化条件为空气气氛下850℃焙烧2 h.     

3D printing of NiZn ferrite architectures with high magnetic performance for efficient magnetic separation

Magnetic materials with desired architectures and high performance have become increasingly important for applications. In this work, NiZn ferrites with mesh structures have been successfully fabricated from preliminary precursors by three-dimensional (3D) printing accompanied by the solid-state reaction. The influence of compositions on structural and magnetic properties of NiZn ferrites were systematically investigated. It was obvious that the saturation magnetization was significantly enhanced to 77 emu/g for NiZn ferrites with a zinc concentration of 0.4, which was a much higher value compared to Ni ferrites. This is attributed not only to the well-known cationic distribution, but also to the grain growth with extraordinarily high crystallinity. Consequently, NiZn ferrites with intricate mesh structures were utilized for magnetic separation, and the distributions of magnetic flux density were simulated. Overall, the fabrication of NiZn ferrites by 3D printing is attractive for scaled-up applications, and also paves the promising avenue for magnetic separation.     

The microstructures, magnetic properties and impedance analysis of Mn–Zn ferrites doped with B2O3

The relationship between the microstructure, magnetic properties and impedance spectroscopy of Mn–Zn ferrites doped with B₂O₃ (up to 0.5 wt.%) has been further investigated. The ferrites were prepared by using a citrate gel processing route. A uniform microstructure with relatively small grains (9.6±0.7 μm) is observed for undoped ferrites (boron-free), which enables good magnetic properties to be achieved (initial permeability μ_i is 2400, power loss P_L is 26.3 kW/m³ at 100 mT).The results on the samples doped with B₂O₃ show that the doping does not benefit the magnetic properties of these gel-derived ferrites, but it promotes grain growth significantly. Discontinuous grain growth at low doping levels (<0.2 wt.%) results in poor magnetic properties. A maximum value of the initial permeability (μ_i: 2600) and a second minimum value (37.2 kW/m³ at 100 mT) in power loss are obtained at the 0.25 wt.% B₂O₃ doping level when the sample has a relatively uniform microstructure with larger grain size (39.5±3.3 μm). With further increases in B₂O₃ doping (0.5 wt.%), the increased porosity and presence of a B-rich phase result in deteriorated magnetic properties. The results of impedance measurement are closely related to the changes in the microstructure which result from these B₂O₃ additions. By using two models for impedance measurement analysis (The Koops’ model and the simple model), the contributions of B₂O₃ to grain boundary resistivity and bulk resistivity can be separated. It is shown that, whilst B₂O₃ has previously been considered to act as only a grain boundary additive, the impedance analysis indicates that both boundary resistivity and grain (bulk) resistivity are increased, thus implying the possible solution of some B₂O₃ within the ferrite spinel structure or an effective change in composition of grain as result of presence of B₂O₃ at the grain boundaries.     

Magnetic and Magnetostrictive Properties of Magnesium-Nickel Ferrites

The purpose of this study was to determine whether or not the magnetic and magnetostrictive properties of mixed Ni-Mg ferrites having various compositions were superior to those of a simple Ni ferrite. The preparation of the ferrites and the test methods are described briefly. The properties tested were Young's modulus, the remanence, the coercivity, the reversible permeability, the static magnetostriction, the electromechanical coupling coefficient, and the dynamic magnetostrictive constant. The results of the tests showed that the Ni ferrite was superior to the Ni-Mg ferrites as far as magnetic and magnetostrictive properties were concerned.     

Microstructure and Properties of Ferrites

Microstructure significantly affects the magnetic and electrical properties of ferrites. Domain behavior and its relation to microstructure of magnetic materials are reviewed, and the critical grain size necessary to maintain a single domain in nickel ferrite is calculated. Experimental data are given for BaO. 6Fe₂ O₃ and NiFe₂O₄ to show the relations among grain sue, coercive force, permeability, ferromagnetic resonance line width (ΔH) , and dielectric losses. Predictions are made for the role of ferrites in the future of ceramic research.     

Microstructural and magnetic evolution of MnZn/FeSiAl composites synthesized by mechanochemistry

Spinel MnZn ferrites (MZFs) were synthesized by solid-state reaction via mechanochemical method. Microwave absorbing composites were fabricated with MZFs and FeSiAl powders. Microstructural evolutions and the influence of MZFs content on magnetic properties, shielding efficiency and reflection loss of composites were investigated. Sintering at 1200 °C, spinel MZFs can be synthesized. With increasing MZFs content, saturation magnetization decreased from 106.94 to 89.71 emu/g. For shielding efficiency and reflection loss, the optimal MZFs content is 10 wt%, the total shielding efficiency reaches to 45 dB. The bandwidth of reflection loss which exceeding −10dB reaches to 4.6 GHz. With increasing it to 15 wt%, the minimum reflection loss can reach to −16.5 dB, but the bandwidth narrowed. The attenuation coefficient decreased with increasing MZFs content.     

Effects of Porosity and Grain Size on the Magnetic Properties of NiZn Ferrite

The effects of porosity and grain size on the magnetic properties of NiZn ferrites were examined on groups of specimens with controlled porosity and grain size; both the permeability and the B-H loop were measured. The demagnetizing factor, which is proportional to porosity, was estimated on the basis of the permeability-porosity relation determined. The discussion of the permeability-grain size relation takes into consideration the dependence of domain wall spacing on grain size. The experimental results for the B-H loops indicate that the remanent magnetic flux density is independent of grain size and the coercive field is independent of porosity. Both the remanent magnetic flux density-porosity and the coercive field-grain size relations are explained via the formulas proposed.     

Influence of SiO2 and CaO additions on the microstructure and magnetic properties of sintered Sr-hexaferrite

The effect of simultaneous addition of CaO and SiO₂ on the microstructure and magnetic properties of sintered SrO-excess Sr-hexaferrites was studied. Both additives markedly affect the grain growth behavior and the magnetic properties. CaO-additions promote densification, which results in increased remanence, but due to simultaneuous grain growth the coercivity drops to <100 kA/m. SiO₂ additions are known to suppress grain growth. Simultaneous addition of CaO and SiO₂ is shown to be very beneficial in tailoring a dense microstructure with relatively small grains. The ratio of CaO/SiO₂ was found to be optimum at about 1, and magnets with a remanence of 430 mT and a coercivity of 300 kA/m were obtained. Transmission electron microscopy (TEM) studies and investigations by energy-dispersive analysis of X-rays (EDX) in the scanning TEM (STEM) mode show that both CaO and SiO₂ are concentrated at grain boundaries and grain junctions forming an amorphous secondary phase.