Ni-Zn Ferrite Research Articles

Tuning the Photocatalytic Performance of Ni-Zn Ferrite Catalyst Using Nd Doping for Solar Light-Driven Catalytic Degradation of Methylene Blue

In this paper, we describe the creation of a moderate band gap Nd-substituted Ni-Zn ferrite as a nano photo catalyst via a simple and cost-effective process of solution combustion. Nd substitution alters the crystallite size, shape, band gap, and magnetic characteristics of Ni-Zn ferrite significantly. Investigations using X-ray diffraction revealed that all samples display a pure phase. The average crystallite size was determined to be between 31.34 and 38.67 nm. On Nd doping, morphology investigations indicated that the shape of nanoparticles changed from approximately spherical to stacked grains. Band gap experiments confirmed the red shift in optical band gap on Nd doping. The synthesized catalysts Ni0.5Zn0.5Fe2O4 (Nd0), Ni0.5Zn0.45Nd0.05Fe2O4 (Nd1), and Ni0.5Zn0.5Nd0.05Fe1.95O4 (Nd2) have been effectively used for the degradation of methylene blue dye under the solar light irradiation. The sample with Nd substitution on Fe sites had the highest methylene blue degradation efficiency. Nd2 photo catalyst degrades the methylene blue dye with a degradation efficiency of 98% in 90 min of solar light irradiation. The photocatalytic activity is triggered by the existence of oxygen vacancies and a mixed valence state of Ni, Fe, and Nd, as confirmed by the XPS investigation. In addition, the investigations on scavenging reveal that the hydroxyl radical is a reactive component in the degradation process. The degradation route has been investigated in relation to the many potential reactions and discovered reactive substances.

Investigation of dielectric and magnetic properties of AL-800 ferrite

Ferrites are usually used in accelerators for tuning radiofrequency (RF) cavities and in nonreciprocal devices controlling the power flow in RF accelerating systems. The conventional parallel‐biased Ni Zn ferrites employed for varying the frequency of accelerating cavities have the disadvantage of high saturation magnetization (4πMs). Application of the transversely biased yttrium iron garnet (YIG) material in RF tuners promises a significant reduction of power loss compared with systems that use the longitudinal bias. To inject the beam and extract the beam out of the CERN accelerator rings the fast kicker magnets made from ferrite materials must be used. Power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. Investigation of the ferrite electromagnetic properties of materials up to the GHz frequency range is essential for a correct impedance evaluation. This report summarizes an approach for deriving electromagnetic properties as a function of both frequency and temperature of the AL-800 garnet material. This information will be useful for simulating ferrite behaviour under realistic operating conditions.

Influence of the Sintering Method on the Properties of a Multiferroic Ceramic Composite Based on PZT-Type Ferroelectric Material and Ni-Zn Ferrite

This paper presents the research results of multiferroic ceramic composites obtained with three sintering methods, i.e., free sintering FS (pressureless), hot pressing HP, and spark plasma sintering SPS. The multiferroic composite was obtained by combining a ferroelectric material of the PZT-type (90%) and zinc-nickel ferrite (10%). Research has shown that the combination of a magnetic material and ferroelectric materials maintains the multiferroic good ferroelectric and magnetic properties of the composites for all sintering methods. A sample sintered with the HP hot pressing method exhibits the best parameters. In the HP method, the composite sample has high permittivity, equal to 910 (at room temperature) and 7850 (at the phase transition temperature), residual polarization 2.80 µC/cm2, a coercive field of 0.95 kV/mm, and the magnetization of 5.3 and 4.95 Am2/kg at -268 °C and RT, respectively. Optimal technological process conditions are ensured by the HP method, improving the sinterability of the ceramic sinter which obtains high density and proper material compaction. In the case of the SPS method, the sintering conditions do not allow for homogeneous growth of the ferroelectric and magnetic component grains, increasing the formation of internal pores. On the other hand, in the FS method, high temperatures favor excessive grain growth and an increase in the heterogeneity of their size. In obtaining optimal performance parameters of multiferroic composites and maintaining their stability, hot pressing is the most effective of the presented sintering methods.

“Magnetic Ni–Zn ferrite anchored on g-C3N4 as nano-photocatalyst for efficient photo-degradation of doxycycline from water”

In the present work, mixed-spinel ferrite anchored onto graphitic carbon nitride (GCN) was synthesized for mineralization of antibiotic pollutant from waste water. A Z-scheme g-C3N4/Ni0.5Zn0.5Fe2O4 nano heterojunction was fabricated by three step procedure: pyrolysis, solution combustion and mechanical grinding followed by annealing. The prepared photocatlyst was tested for degradation of Doxycycline (DC) drug under the natural sun light. Results revealed that the prepared heterojunction has maximum degradation efficiency of 97.10% pollutant in 60 min experiment. The Z-scheme heterojunction between g-C3N4 and Ni–Zn ferrite improves the photoinduced charges separation and protection of redox capability and therby increases the photo degradation efficiency. The scavenging experiments suggested that O2−● and h+ as main active species responsible for degradation of the antibiotic. In addition, the dopant variation can drive the shists in band gap and energy band positiong too which makes then excellent candidates for synthesizing tunable heterostructures with organic semiconductors. The work focusses on designing and developing of saimpler but efficient magnetic heterojunctions with superior redox capability for solar powered waste water treatment.

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.

Wideband Microwave Photonic Circulator Using Two Asymmetric Partial-Height Triangle Ferrites.

Broadband 5G communication requires the operation of nonreciprocal devices in the Ku band. A wideband photonic crystal circulator is implemented by introducing two partial-height triangular Ni-Zn ferrites into the Al2O3 ceramic rod-arrays. The asymmetric sizes of the two equilateral triangles paired with self-matching effectively extend the bandwidth of the circulator eight times over that of the symmetric scheme. Numerical simulations demonstrate that the photonic crystal circulator can obtain a bandwidth of 1.00 GHz with an isolation 25.75 dB and an insertion loss 0.381 dB through optimized matched triangle size ratio, suitable for applications in future communication systems.

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.

Correlation between the Magnetic and DC resistivity studies of Cu substituted Ni and Zn in Ni-Zn ferrites

Cu substituted Ni0.5-xCuxZn0.5Fe2O4 (x = 0, 0.05, 0.1, 0.15 and 0.2) samples is synthesized using the sol-gel auto-combustion process. They have a cubic spinel structure with crystallite size in the range of 29.01–42.68 nm. The increment in the copper content increases the DC conductivity. The electrical resistivity decrease with an increase in the temperature i.e. it has a negative temperature coefficient with resistance similar to semiconductors. The remnant ratios R obtained from VSM show their isotropic nature forming single domain ferrimagnetic particles. The results are compared with Ni0.5CuxZn0.5-xFe2O4 (x = 0 to 0.25). The resultant material Cu substituted Zn is more significant than that of Ni as indicated by its results and previous literature. BIBECHANA 19 (2022) 61-67

Integrated MEMS Toroidal Transformer With Ni-Zn Ferrite Core for Power Supply on Chip

A miniature integrable transformer is an obstacle to the miniaturization of packaged power supply on chip (PwrSoC). This letter introduces a through-silicon via (TSV) high-aspect-ratio toroidal transformer manufactured using microelectro-mechanical systems and electroplating. The primary coil and secondary coil of the transformer are interleaved on the toroidal core cavity, which is entirely wrapped in silicon, and a 1.2 mm high toroidal Ni-Zn ferrite core is formed. A 15:15 turn transformer is fabricated with a compact coil size of Φ4.1 × 2 mm with an aspect ratio (ratio of TSV depth to diameter) of 20. Measurements show that it has an inductance of 105 to 115 nH in a high frequency range of 1 to 80 MHz and a coupling coefficient of ∼0.7 in the range of 1 MHz to >15 MHz. Compared to that of the transformer without the Ni-Zn ferrite core, the coupling coefficient of the toroidal transformer increases by 40% with an inductance increase of 20%. At a frequency of 14 MHz, the transformer has a maximum quality factor of 16.7. The small size, IC compatible manufacturing process and excellent performance at high-frequency of the transformer proposed, meet the further integrated and miniaturized needs of PwrSoC.

Microwave absorption properties of rare earth (RE) ions doped Mn–Ni–Zn nanoferrites (RE = Dy, Sm, Ce, Er) to shield electromagnetic interference (EMI) in X-band frequency

Sol-gel auto combustion technique has been adopted to prepare RE doped Mn–Ni–Zn ferrite systems following the stoichiometry Mn0.1Ni0.7Zn0.2RE0.5Fe1.5O4 (RE = Dy, Ce, Sm and Er). The XRD patterns confirm the cubic spinel phase with the Fd3m space group and the lattice parameter and crystallite size were found to be in the range of 8.3874–8.4066 Å and 28.6–33.2 nm. The M − H data indicates the soft magnetic behaviour of present ferrite systems. The substitution of rare-earth ions in the spinel structure influences the superexchange interaction and in turn, affects the magnetic behaviour of present ferrite systems. The highest value of saturation magnetization equal to 41.2 emu/g was observed for the sample with a composition of Mn0.1Ni0.7Zn0.2Ce0.5Fe1.5O4. For all the ferrite systems studied here the real part (ε′) of complex permittivity is increasing with an increase in frequency while oscillatory nature can be found in the imaginary part (ε″). The value of ε′ found in the range of 5.421–5.856 at 8.2 GHz and it is 5.538–6.066 at 12.4 GHz. The value of ε″ is in the range of 0.092–0.104 at 8.2 GHz while it is in between 0.042 and 0.105 at 12.4 GHz. A wavy nature can be seen in the real part (μ′) of complex permeability whereas the imaginary part (μ″) is decreasing for all compositions with the increase in frequency, but shows a weak resonance peak between 9 and 10 GHz. The value of μ′ is in the range of 0.869–0.958 at 8.2 GHz and it is 0.903–0.925 at 12.4 GHz. The value of μ″ fall in between 0.269 and 0.334 at 8.2 GHz and it is in the range of 0.059–0.068 at 12.4 GHz. The shielding studies for EMI revealed that the present systems are working as microwave absorbers. The total effective shielding for all ferrite systems is in the range of 33.31–36.09 dB 8.2 GHz while it is in between 32.74 and 34.98 dB at 12.4 GHz. Under the investigation of shielding performance, it is observed that all the RE doped Mn–Ni–Zn ferrites systems studied here can effectively suppress the electromagnetic interference in X-band frequency. The ferrite system with composition Mn0.1Ni0.7Zn0.2Ce0.5Fe1.5O4 has shown a potential microwave absorber in X-band frequency.

Synthesis, structural, magnetic and optical studies of Eu doped Ni–Zn nano ferrites

Ni–Zn ferrites exhibit properties like high resistivity, high Curie temperature, and low relative loss. In this paper, the impact of the small doping of Europium on structural, magnetic and optical properties of Ni–Zn ferrites has been investigated. The samples were prepared through the Sol-Gel method and grounded powders were calcined at 500 °C for 4hrs. Cubic crystalline structure with Fd-3m space group was confirmed for all ferrites by XRD and Ritveld refinement. Surface morphology of the samples was revealed by SEM. The cation distribution and crystal deformation were observed from Raman spectra with increasing Eu3+ ions content. The band gap energy values were calculated from UV–Visible spectra which are in the order of 1.6 eV and these values were directly proportional to the lattice constant. Room temperature magnetic properties were studied and the variation in the properties with the doping was discussed. From magnetic properties of Eu doped Ni–Zn ferrites it was found that these are suitable for core material in transformers and in power transmission.

Investigation of Magnetic Phase Formation in Nickel-Zinc Ferrites by X-Ray Diffraction and Thermal Analysis

The magnetic spinel phase formation in Ni1-xZnxFe2O4 (x=0.1, 0.3, 0.5) nickel-zinc ferrite synthesized from mechanically activated NiO-ZnO-Fe2O3 mixture was studied by thermomagnetometry method, X-ray diffraction and saturation magnetization analyses. The initial reagents were activated via milling the mixture in a planetary ball mill at 500 and 1000 rpm. The Ni-Zn ferrites were synthesized at 950 °C for 4 hours using the solid-state technology. The correlation between the results obtained using above methods of testing ferrite was revealed. It was found that the magnetic spinel phase concentration in the synthesized samples increases with an increase in the milling energy intensity of mixture. Thus, ferrite obtained from pre-activated at 1000 rpm oxides is characterized by a high concentration of nickel-zinc ferrite in their composition.

The effect of microstructure on the initial permeability of Ni-Zn ferrite

We have studied the sintering behavior, microstructure, and permeability of the ferrite Ni0.50Zn0.50Fe2O4 sintered at temperatures from 1000 °C to 1400 °C for various dwell times. The shrinkage rate is maximum at 1140 °C; hence samples sintered at T ≥ 1100 °C exhibit densities larger than 97%. Moderate grain growth is observed up to 1250 °C; however, if the density exceeds a threshold of 98% enhanced grain growth sets in. All samples are single-phase spinels with the lattice constant slightly increasing with sintering temperature. At T ≥ 1300 °C significant ZnO evaporation sets in and the corresponding change in ferrite composition is indicated by mass loss, EDX-analysis, and Seebeck coefficient measurements. The complex permeability spectra show systematic changes with sintering temperature and dwell time. For samples sintered at 1100 °C, the permeability increases from µ’=133 for a dwell time of 30 min to µ’=318 after 24 h sintering. The variation of the permeability is discussed as function of density and grain size. The non-magnetic grain boundary model is applied to interpret the grain size dependence of the permeability.

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.

Useful High-Entropy Source on Spinel Oxides for Gas Detection.

This study aimed to identify a useful high-entropy source for gas detection by spinel oxides that are composed of five cations in nearly equal molar amounts and free of impurities. The sensor responses of the spinel oxides [1# (CoCrFeMnNi)3O4, 2# (CoCrFeMnZn)3O4, 3# (CoCrFeNiZn)3O4, 4# (CoCrMnNiZn)3O4, 5# (CoFeMnNiZn)3O4, and 6# (CrFeMnNiZn)3O4] were evaluated for the test gases (7 ppm NO2, 5000 ppm H2, 3 ppm NH3, and 3 ppm H2S). In response to NO2, 1# and 2# showed p-type behavior while 3–6# showed n-type semiconductor behavior. There are three p-type and one n-type AO structural compositions in AB2O4[AO·B2O3] type spinel, and 1# showed a stable AO composition because cation migration from site B to site A is unlikely. Therefore, it was assumed that 1# exhibited p-type behavior. The p-type behavior of 2# was influenced by Cr oxide ions that were present at the B site and the stable p-type behavior of zinc oxide at the A site. The spinel oxides 3# to 6# exhibited n-type behavior with the other cationic oxides rather than the dominant p-type behavior exhibited by the Zn oxide ions that are stable at the A site. In contrast, the sensor response to the reducing gases H2, NH3, and H2S showed p-type semiconductor behavior, with a particularly selective response to H2S. The sensor responses of the five-element spinel oxides in this study tended to be higher than that of the two-element Ni ferrites and three-element Ni-Zn ferrites reported previously. Additionally, the susceptibility to sulfurization was evaluated using the thermodynamic equilibrium theory for the AO and B2O3 compositions. The oxides of Cr, Fe, and Mn ions in the B2O3 composition did not respond to H2S because they were not sulfurized. The increase in the sensor response due to sulfurization was attributed to the decrease in the depletion layer owing to electron sensitization, as the top surface of the p-type semiconductors, ZnO and NiO, transformed to n-type semiconductors, ZnS and NiS, respectively. High-entropy oxides prepared using the hydrothermal method with an equimolar combination of five cations from six elements (Cr, Mn, Fe, Co, Ni, and Zn) can be used as a guideline for the design of high-sensitivity spinel-type composite oxide gas sensors.

Co substituted Ni–Zn ferrites with tunable dielectric and magnetic response for high-frequency applications

Microwave ferrites are the most promising materials for high frequency and high-power devices. In this work, Co substituted Ni–Zn ferrites (Ni0.5-xZn0.5CoxFe2O4; x = 0–0.4) are synthesized, and the structural, morphology, dielectric, magnetic response are systematically investigated. The X-ray diffraction pattern (XRD) pattern confirmed the formation of pristine cubic phase alone without any secondary phase in all the samples. Substitution of Co2+ resulted in increased crystallite size and lattice constant. Raman peak intensity is suppressed, and a shift towards a lower wavenumber is observed with Co substitution. The change in position and intensity is analyzed and attributed to the change in cationic distribution in tetrahedral and octahedral positions by deconvoluting the Raman peaks. The Energy-dispersive X-ray spectroscopy (EDAX) analysis confirms the stoichiometry of compounds. The real permittivity and tan δ are decreased with the dilution of Co (x = 0: ε' = 24, tan δ = 0.015; x = 0.4: ε' = 11, tan δ = 0.035 @ 1 MHz). Further, permeability initially increased in the X band frequency range and decreased with increasing Co concentration. An increase in the saturation magnetization was observed initially with increased Co content and a decrease after x = 0.2. A maximum saturation magnetization (Ms = 63.3 emu/g) observed for x = 0.2 composition. Interestingly, a giant coercivity and high effective magnetocrystalline anisotropy are observed with the incorporation of Co at low temperatures (5 K). The low dielectric loss, high saturation magnetization, and low coercivity at room temperature of Co substituted Ni–Zn ferrites suggest that these compounds are potential candidates for high-frequency devices (circulators).

RF Pulse Generation in a Gyromagnetic Nonlinear Transmission Line With Periodically Placed Ferrites and Permanent Magnets

This article presents a work on development of a high-power radio pulse generator, which is a gyromagnetic nonlinear transmission line (GNLTL) in which periodically placed NiZn ferrites are saturated by an axial magnetic field produced by permanent magnets periodically placed inside the transmission line. Structurally, the line is a corrugated coaxial waveguide with permanent NdFeB magnets placed inside the inner conductor of the line. The transmission line geometry was optimized using numerical simulation by finite-difference time domain (FDTD) method. The excitation of high-frequency oscillations in the developed transmission line at central frequency of 1 GHz and above is shown experimentally using ferrite rings with 45 and 28 mm outer and inner diameters. The maximum peak power of microwave oscillations obtained in the experiments is 110 MW at the central frequency 1.3 GHz. The obtained RF power is comparable to that of more common GNLTL with continuous filling by ferrite rings having the same transverse size.

Comparative study of microwave absorption properties of Ni–Zn ferrites obtained from different synthesis technologies

Spinel ferrites are widely used for electromagnetic wave (EMW) absorption applications. In this study, spinel Ni–Zn ferrites with excellent microwave absorption properties were synthesized. Their EMW absorption characteristics and interaction mechanisms were studied to lay the foundation for the study of the role of Ni–Zn ferrite as a magnetic substrate for composites. Herein, Ni0·5Zn0·5Fe2O4 was prepared by the hydrothermal method (H-NZFO) and the sol–gel auto-combustion method (S-NZFO); both samples exhibited distinct microwave absorption properties. The S-NZFO absorber (thickness = 3.72 mm) demonstrated the best dual-zone microwave absorption with two strong reflection loss peaks at 5.1 and 10.5 GHz. The corresponding effective absorption bandwidth (EAB) reached 9.0 GHz, which covered part of the S-band and all of the C- and X-bands. These results were attributed to the high saturation magnetization, outstanding complex permeability, and multiple magnetic loss channels of S-NZFO. The H-NZFO sample exhibited excellent absorption capability and matching thickness. At a thickness as low as 1.71 mm, the minimum reflection loss (RLmin) of the H-NZFO absorber reached -60.2 dB at 13.1 GHz. The maximum bandwidth corresponding to RL below -10 dB was 4.6 GHz. These results can be attributed to small particle size, high complex permittivity, and multiple dielectric loss channels of H-NZFO. The observed wide effective absorption bandwidth of S-NZFO and strong microwave absorption capability of H-NZFO suggest the potential of both materials as substrates for efficient microwave absorbers in military as well as civilian absorption applications.

Facile synthesis and enhanced microwave absorption of C@Ni0.5Zn0.5Fe2O4 shell-core structured nanoparticles

C@Ni0.5Zn0.5Fe2O4 nanoparticles with different annealing temperatures and shell-core mass ratios were synthesized by a tannic acid coating method. Through SEM, TEM, EDS and XRD characterization, the as-prepared product was confirmed to be shell-core structured C@Ni0.5Zn0.5Fe2O4 nanoparticles with an average diameter of approximately 650 nm, and a carbon layer was deposited on the surface of the product. Compared with uncoated NiZn ferrite, the carbon-coated NiZn ferrite exhibits a moderate real part and imaginary part of its complex permittivity, while maintaining high permeability, which improves the impedance matching characteristics and microwave loss performance of the material. When the shell-core mass ratio was 9:1 and the annealing temperature was 900 °C, the as-prepared sample exhibited advanced microwave absorption performance with a minimum reflection loss (RL) of -26.87 dB at 4.3 GHz with a matching thickness of 1.8 mm, and the effective absorptive bandwidth was approximately 4.05 GHz when the RL was below -10 dB.