Ferrite Ceramics Research Articles

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.

Properties of Perovskite-like Lanthanum Strontium Ferrite Ceramics with Variation in Lanthanum Concentration

The purpose of this work is to study the effect of lanthanum (La) concentration on the phase formation, conductivity, and thermophysical properties of perovskite-like strontium ferrite ceramics. At the same time, the key difference from similar studies is the study of the possibility of obtaining two-phase composite ceramics, the presence of various phases in which will lead to a change in the structural, strength, and conductive properties. To obtain two-phase composite ceramics by mechanochemical solid-phase synthesis, the method of the component molar ratio variation was used, which, when mixed, makes it possible to obtain a different ratio of elements and, as a result, to vary the phase composition of the ceramics. Scanning electron microscopy, X-ray phase analysis, and impedance spectroscopy were used as research methods, the combination of which made it possible to comprehensively study the properties of the synthesized ceramics. Analysis of phase changes depending on lanthanum concentration change can be written as follows: (La0.3Sr0.7)2FeO4/LaSr2Fe3O8 → (La0.3Sr0.7)2FeO4/LaSr2Fe3O8/Sr2Fe2O5 → (La0.3Sr0.7)2FeO4/Sr2Fe2O5. Results of impedance spectroscopy showed that with an increase in lanthanum concentration from 0.10 to 0.25 mol in the synthesized ceramics, the value of the dielectric permittivity increases significantly from 40.72 to 231.69, the dielectric loss tangent increases from 1.07 to 1.29 at a frequency of 10,000 Hz, and electrical resistivity decreases from 1.29 × 108 to 2.37 × 107 Ω∙cm.

Investigation of the ion dynamics by a particular excitation due to the stoichiometric imbalances on BiFeO[formula omitted] ceramics

In this work, bismuth ferrite ceramics have been synthesized with various stoichiometric imbalances by the pressure-less sintering technique. UV–Vis spectroscopy and scanning electron microscopy show that both the band gap and the grain morphology of the ceramics are comparable to the stoichiometric imbalances. More necessarily, excess iron in the stoichiometry shows new charge carrier dynamics with the existence of completely new crystalline biferroic Bi1.2Fe0.8O3+δ ceramics. This means the iron ion valence fluctuation is well tailored by modifying iron contents. The conductivity study explains that two discrete forms of Johnscher’s power law and Super-linear power law types of conductivity mechanism can be induced by the change of stoichiometry. Obtained outcomes illustrate that stoichiometric imbalances play a major role in ion dynamics, leading to identifying a new path to engineer the properties of bismuth ferrite ceramics.

Highly responsive photodetection based on bismuth ferrite ceramics: The roles of depolarization field and domain network

This study presents the highly-sensitive, millisecond-response, and self-powered photosensors based on the indium-tin-oxide (ITO)/Bi0.93R0.07FeO3 ceramic/Au heterostructures (R = Nd, Gd) at 360-nm irradiation. Photocurrent density (Jph), photoconductive gain (G), photoresponsivity (R) and specific detectivity (D*) were significantly boosted by an electric-field poling, and can reach 1.4 mA/cm2, 25%, 71 mA/W and 2.4 × 1011 Jones in the ITO/Bi0.93Gd0.07FeO3/Au; 0.17 mA/cm2, 14.5%, 42 mA/W and 2.6 × 1012 Jones in the ITO/Bi0.93Nd0.07FeO3/Au. Fast response times of 0.6 ms and 1.0 ms are respectively detected in the ITO/Bi0.93Gd0.07FeO3/Au and ITO/Bi0.93Nd0.07FeO3/Au. The enhanced photodetection is driven collectively by the p-n heterojunction, the depolarization field, and the electric-field-induced domain-wall nucleation. The complex network consisting of grain boundaries and nanoscale domain walls provides electrically conductive passages in the grain matrix. This work delivers an energy self-sufficient route using the polycrystalline rare-earth-doped BiFeO3 ceramics for the high-performance photodetection in the ultraviolet-A spectrum.

Synthesis of a magnetically removable visible-light photocatalyst based on nickel-doped zinc ferrite

In this study, a facile method to synthesize magnetically removable visible-light photocatalysts based on nickel-doped zinc ferrites is presented. Ferrite semiconductor ceramics with the general formula Zn1-xNixFe2O4 (0 ≤ x ≤ 0.5, Δx = 0.1) were prepared by high-energy ball milling followed by annealing at 873 K. X-ray diffraction analysis confirmed the spinel single-phase Fd-3m without secondary phases for all compositions. The slight decrease in lattice parameters confirmed the presence of Ni2+ ions in the crystal structure because Ni had a smaller ionic radius than Zn. Raman spectroscopy demonstrated that Ni2+ ions were distributed on both tetrahedral and octahedral sites, which increased the inversion parameter and affected the photocatalytic efficiency and ferromagnetism. Magnetic hysteresis loops suggested an increase in the specific magnetization as the doping content increased, enabling magnetic recovery and reuse of the photocatalyst in water remediation. Diffuse reflectance spectroscopy showed a reduction in the band gap values with increasing nickel content, which was attributed to forming a sub-level in the band structure in the presence of Ni2+. Photocatalytic tests revealed a degradation efficiency higher than 60%, confirming that the doped samples obtained by high-energy ball milling were highly efficient and easily removable photocatalytic materials.

Modulating self-biased near-UV photodetection of Gd-doped bismuth ferrite ceramics by introducing zinc oxide as electron transport layer

ZnO semiconductor offers many advantages as an electron transport layer (ETL) in photovoltaic-based devices, including high charge carrier mobility and hole-blocking ability. In this work, ZnO thin film is introduced as an ETL between (Bi0.93Gd0.07)FeO3 (BFO7Gd) ferroelectric and ITO thin film to form ITO/ZnO/BFO7Gd/Au heterostructure. The device with the ETL exhibited a superior photoresponsivity than the one without ETL, reaching ∼32% enhancement. Furthermore, a subsequent E-field poling on the ITO/ZnO/BFO7Gd/Au heterostructure resulted in an additional ∼25% increase in photoresponsivity. The enhancement is mainly attributed to two factors: (1) high electron mobility and lower recombination rate resulting from the introduction of ZnO ETL, and (2) efficient charge separation facilitated by the polarization-driven internal E field that superimposes with the interfacial built-in E fields. The introduction of ZnO ETL and the utilization of the ferroelectric polarization prove to be an alternative route to further modulate the photosensing performance of BiFeO3-based near-UV photodetectors.

Effect of pH value on multiferroic properties of barium ferrite ceramics prepared by sol–gel method

In this paper, BaFe12O19 (BaM) ceramics at different pH values were prepared by sol–gel method. Effects of pH value on the microstructure, electrical as well as magnetic properties were systematically studied. XRD indicate that the ceramics were mainly BaM. However, with the pH value increasing further, the BaFe2O4 impurity phase appears gradually in both powders and ceramics due to the degree of complexation between citric acid and metal cations and other reasons. SEM results show that the grain size of ceramics decreases from 2.28 μm to 1.35 μm with the pH value increase from 4 to 8. It is found that room temperature dielectric constant, residual polarization, and saturation magnetization of the ceramics is the largest when the pH value of the solution is 4, which are 0.108 μC/cm2 and 32.829 emu/g, respectively. The dielectric constant and residual polarization of ceramics decrease with the increase of pH value. The ferroelectric and magnetic hysteresis loops have confirmed room-temperature multiferroic properties of the prepared ceramics. It laid the foundation for the further development of new room temperature single-phase multi-iron materials.

Effect of sintering temperature on magnetoelectric properties of barium ferrite ceramics

Effect of sintering temperature on magnetoelectric properties of barium ferrite ceramics

Chemical homogeneity, microstructure and magnetic properties of LiTiZn ferrite ceramics doped with Al2O3 or ZrO2

Sintering of ferrite materials requires sensitive control of homogeneity that affects electromagnetic properties. The paper proposes a method for analysis of chemical homogeneity of ferrite ceramics based on mathematical analysis of differential temperature dependences of the initial permeability near the Curie point. The method was tested on model samples of LiTiZn ferrite ceramics doped with Al 2 O 3 or ZrO 2 of 0.10, 0.25, 0.5 0.75, and 1 wt%. It was found the effect of doping agents on the ferrite lattice parameter is insignificant, and they are not indicated on the diffraction patterns as separate peaks. SEM data show a weak effect of Al 2 O 3 doping agent on the average grain size of ferrite ceramics. At the same time, the effect is more pronounced for ZrO 2 due to secondary recrystallization. In this case, the coercive force shows a particular increase as compared with undoped samples: by 23% and 60% for Al 2 O 3 and ZrO 2 respectively of doping agents’ concentration increased to 1 wt%. The paramagnetic-to-ferrimagnetic transition of ferrites near the Curie point is highly sensitive to chemical homogeneity of the material. It was shown that the width of the differential temperature dependence peak of the initial permeability can be used to assess chemical homogeneity of ferrimagnetic ceramics. The peak width was found to increase by 75%. Therefore, the proposed method revealed a higher sensitivity compared to XRD and hysteresis loops. • The study revealed the effect of doping agents Al 2 O 3 or ZrO 2 on microstructural and magnetic properties of LiTiZn ferrites. • The paramagnetic transition of ferrites is characterized by the rate of the decrease in the initial permeability. • The transition highly sensitive to chemical homogeneity of LiTiZn ferrite ceramics. • A highly sensitive method has been developed for analysis of chemical homogeneity. • A decrease in the peak width is the most sensitive characteristic of chemical homogeneity increases.

Facile microwave-assisted synthesis of magnetic ferrite: Rapid interfacial reaction underlying intensifying mechanism

Microwave-assisted (MW-assisted) heating is clean and intensively used to synthesize materials owing to the high-efficiency volumetric and selective heating modes. In the current paper, a design and facile synthesis of magnetic ferrite ceramics by microwave-assisted heating of MnO2 and Fe2O3 was conducted to reduce the synthetic temperature of conventional heating. The microwave absorptivity and temperature rise characteristics of the MnO2–Fe2O3 system were first assessed for the material design of MnFe2O4, and then the phase transformation, microstructure evolution, and magnetism change of the MnO2–Fe2O3 system heated under conventional and MW-assisted heating were compared. Investigations on electromagnetic properties and heating behaviors of MnO2–Fe2O3 mixture suggested that a suitable cylinder sample size for microwave heating was designed to be 10 mm in diameter and 10 mm in length based on the dielectric loss and magnetic hysteresis loss of microwave penetration at different depths. The intensifying mechanism for microwave heating was associated with the rapid interfacial reaction between MnO2 and Fe2O3. Under microwave irradiation at 935 °C, some perfectly crystallized MnFe2O4 was preferentially formed at the interface of MnO2 and Fe2O3, and these MnFe2O4 were evenly distributed in the cylinder samples. Similar to the “self-propagating” effect, the in-situ generation of MnFe2O4 with good energy conversion ability evenly distributed everywhere of the cylinder would facilitate the reaction of MnO2 and Fe2O3 under microwave irradiation based on the distinctive selective and volumetric heating. Compared with conventional heating at 1200–1250 °C, ferrite synthetic temperatures via MW-assisted heating decreased to 900–1000 °C, and the low-temperature synthesis of ferrite also had a good electromagnetic performance. Eventually, the clean and value-added utilization of low-grade ferruginous manganese ores via MW-assisted heating was validated for the preparation of manganese ferrite from minerals under reduced roasting temperatures.

Influence of the Cooling Rate at Thermal Sintering on the Structure and Magnetic Properties of Ferrite Ceramics

The influence of the cooling rate during sintering of lithium-titanium-zinc-manganese spinel ferrite on its structural, magnetic and electric characteristics was studied. The ferrite was sintered in air at 1283 K for 120 min. Cooling rates were 0.06 K/s and 7.8 K/s. It was established that the observed changes in the characteristics when using slow and quenching cooling are due to the different levels of the near-surface ferrite layers oxidation. For quench ferrite, the Curie temperature of 530 K, the activation energy of electrical conductivity of 0.35 eV in the bulk of the samples, and the magnetic anisotropy constant of 2.6·10-3 J/m3 (at 300 K) were obtained. Slowly cooled ferrite was characterized by higher values of Curie temperature (560 K), the magnetic anisotropy constant (2.9·10-3 J/m3), and the activation energy of electrical conductivity (0.80 eV).

Manipulating resonances and absorptions of terahertz ferrite ceramics

Ferrites are widely used in the preparation of basic components that function within the microwave band. Compared with ferromagnetic ferrites, which possess a weak internal anisotropy field so that the working frequency of ferrite ceramics cannot be increased into the terahertz band, antiferromagnetic rare earth orthoferrites undergo strong interactions on the order of 100 T so that terahertz (THz) resonances can be supported. However, the zero or near-zero magnetization and internal dipolar fields complicate the manipulation of the THz responses in antiferromagnets using the traditional magnetic method. In this article, we choose PrFeO3 as a model of rare earth orthoferrites and report a method of cooling and thickening to tune the THz resonances and absorptions. A combination of tuned time- and frequency-domain spectroscopic responses, including variations in amplitude with the time delay, changes in the transmittance, the peak height, the extinction coefficient κ, dissipation factor tanδ, and absorption coefficient α, which varied with frequency, reveal that our approach is effective. In this work, the resonant frequency of ferrites is promoted to the THz band, providing a highly effective approach for exciting and tuning their resonances and absorptions and offering support for the application of ferrite ceramics in the field of terahertz devices.

Synergistic effect of V2O5 and Bi2O3 on the grain boundary structure of high-frequency NiCuZn ferrite ceramics

High-frequency soft magnetic ferrite ceramics are desired in miniaturized and efficient power electronics but remain extremely challenging to deploy on account of the power loss (Pcv) at megahertz frequencies. Here, we prepared NiCuZn ferrite with superior high-frequency properties by V2O5 and Bi2O3 synergistic doping, which proves to be a potent pathway to reduce Pcv of the ferrite at megahertz frequencies. The sample doped with 800 ppm V2O5 and 800 ppm Bi2O3 yielded the most optimized magnetic properties with a Pcv of 113 kW/m3 (10 MHz, 5 mT, 25 °C), an initial permeability (μi) of 89, and a saturation induction (Bs) of 340 mT, which is at the forefront of the reported results. These outstanding properties are closely related to the notable grain boundary structure, which features a new type of nano-Bi2Fe4O9 phase around ferrite grains and a Ca/Si/V/O amorphous layer. Our results indicate great strides in correlating the grain boundary structure with multiple-ion doping and set the scene for the developing high-frequency soft magnet ferrites.

Effect of lanthanum substitution on structural, magnetic, and electric properties of Ni–Zn–Co ferrites for radio frequency and microwave devices

In this study, Ni0.55Zn0.3Co0.15LaxFe2−xO4 (x = 0, 0.05, 0.10, 0.15, and 0.20) ferrite ceramics with low magnetic loss and high resonant frequency were prepared. As La3+ ion content was increased, the real part of the dielectric constant (ε′) and dielectric loss was greatly reduced. The DC resistivity was as high as 4.5 × 106 Ω m (x = 0.15). The saturation magnetization (Ms) reduced from 76.1 to 58.4 emu/g, the coercivity (Hc) increased from 42.3 to 58.1 Oe, and the magnetic quality factor (Q) increased by 33%. More importantly, the resonance frequency of the La3+-substituted ferrite samples also increased with increasing La3+ ion content. The peak frequency of Q increased from 60 to 368 MHz, which is 7–10 times higher than that of other ferrites. In general, the substitution of Ni–Zn–Co ferrite with rare earth La3+ ions broaden the application of ferrite ceramics in the field of radio frequency and microwave devices.

Polarization-sensitive UVA photodetector based on heterojunction of ITO and rare-earth doped bismuth ferrite ceramics

Ferroelectric photovoltaic materials have been subjected to intensive research in view of their applications for high-performance self-biased UV photodetectors. This work reports the ferroelectric polarization-enhanced near-UV (λ = 405 nm) and UVA (λ = 360 nm) photoresponse of the indium-tin-oxide (ITO)/(Bi0.93Sm0.07)FeO3/Pt and ITO/(Bi0.93Gd0.07)FeO3/Pt heterostructures. A superior photoresponse was observed in the ITO/(Bi0.93Gd0.07)FeO3/Pt device with photoresponsivity of ∼7.3×10−2A/W, specific detectivity of ∼2.5×1011Jones, and response times of τr ∼1 ms and τd ∼1 s under 360-nm light illumination. The photocurrent generation is facilitated by the interfacial E fields and ferroelectric polarization-induced E field. The improved photosensing ability is ascribed to the collective effect of the electric field-enhanced interaction between oxygen 2p and Fe 3d orbitals and the interconnection of grain boundaries and domain walls that plays roles of charge transport paths. (Bi0.93Gd0.07)FeO3 exhibited a more superior photoresponse than (Bi0.93Sm0.07)FeO3 due to its more complex domain structure, smaller bandgap, and stronger orbital hybridization. These results demonstrate the feasibility of utilizing the ferroelectric polarization and domain structure in (Bi0.93Gd0.07)FeO3 to enhance photodetection, thus providing a route for the realization of a highly sensitive and self-biased visible-UVA photodetector.

High-entropy spinel ferrites MFe2O4 (M = Mg, Mn, Fe, Co, Ni, Cu, Zn) with tunable electromagnetic properties and strong microwave absorption

Ferrites are the most widely used microwave absorbing materials to deal with the threat of electromagnetic (EM) pollution. However, the lack of sufficient dielectric loss capacity is the main challenge that limits their applications. To cope with this challenge, three high-entropy (HE) spinel-type ferrite ceramics including (Mg0.2Mn0.2Fe0.2Co0.2Ni0.2)Fe2O4, (Mg0.2Fe0.2Co0.2Ni0.2Cu0.2)Fe2O4, and (Mg0.2Fe0.2Co0.2Ni0.2Zn0.2)Fe2O4 were designed and successfully prepared through solid state synthesis. The results show that all three HE MFe2O4 samples exhibit synergetic dielectric loss and magnetic loss. The good magnetic loss ability is due to the presence of magnetic components; while the enhanced dielectric properties are attributed to nano-domain, hopping mechanism of resonance effect and HE effect. Among three HE spinels, (Mg0.2Mn0.2Fe0.2Co0.2Ni0.2)Fe2O4 shows the best EM wave absorption performance, e.g., its minimum reflection loss (RLmin) reaches −35.10 dB at 6.78 GHz with a thickness of 3.5 mm, and the optimized effective absorption bandwidth (EAB) is 7.48 GHz from 8.48 to 15.96 GHz at the thickness of 2.4 mm. Due to the easy preparation and strong EM dissipation ability, HE MFe2O4 are promising as a new type of EM absorption materials.

Overlapping large polaron tunnelling (OLPT) type conduction mechanism in magnesium ferrite (MgFe2O4) ceramics

Overlapping large polaron tunnelling (OLPT) type conduction mechanism in magnesium ferrite (MgFe2O4) ceramics

Tailoring the magnetic properties of Zn doped nickel, magnesium and cobalt ferrite ceramics

Zinc substituted cobalt, magnesium and nickel ferrites (M(1−x)ZnxFe2O4, x = 0.0, 0.5) were prepared using combustion reaction techniques. The particle sizes were roughly round shaped with 1 μm dimensions. The Zn2+ substitution led to the increase in the crystal parameters with higher densities. The band shift in FTIR spectra was observed at 600 cm−1 for the A-site doping. The obtained magnetic measurement results have demonstrated the effect of zinc substitution preferably in tetrahedral site on all the ferrites. More precisely, the maximum saturation magnetization and anisotropy value were observed for the Co–CoZn pairs. The magnetic parameters variation was presented through Yafet and Kittel model with the help of change in geometry of the interaction between A-B sites. Keywords: Spinel ferrite; A-B super-exchange; magnetic properties; high entropy oxides; Rietveld refinement.

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

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

Boosting the performance of magneto-mechano-electric energy generator using magnetic lens

Herein, we introduce a concept of the magnetic lens, which were composed of high permeability ceramic ferrites, to enhance the output performance of Magneto-Mechano-Electric (MME) energy generator. The magnetic lens was found to enhance the output voltage of MME generator by concentrating the weak magnetic flux originating from the magnetic field sources onto magnetic constituents in MME structure. The feasibility of the use of the magnetic lens as a magnetic flux concentrator was first evaluated by using Finite Elemental Analysis. The simulation results are then experimentally verified by harvesting the weak fields originating from the Helmholtz coil. Depending on the configuration of magnetic lens, the output of MME was different. The MME generator with a magnetic lens composed of four ferrites exhibited enhancement of 288% and 125% over that of MME generator without a lens and with a lens composed of one ferrite, respectively.