Ferrite Ceramics Research Articles

Synthesis, electrical and IR spectroscopy of Calcium substituted Yttrium ferrite ceramics

The single-phase polycrystalline ceramic samples of Y1-xCaxFeO3 (x = 0.03 & 0.05) have been prepared by the conventional high temperature solid state reaction method. The X-ray diffractogram confirmed the orthorhombic symmetry with space group Pnma. The dielectric and impedance analysis have been done for both these samples as a function of frequency (from 100 Hz to 5 MHz) and temperature (from RT to 673 K). The IR spectra have been recorded in the transmission mode in fingerprint region (700 cm−1 to 400 cm−1) using Fourier Transform Infrared Spectroscopy (FTIR). Various vibrational parameters have been calculated for Fe–O bond. The results are discussed in detail.

Monitoring structural variation on Gd ratio of La modified bismuth ferrite ceramics with enhanced magnetization

Critical structural variation and dielectric properties were investigated in Lanthanum and Gadolinium co-substituted bismuth ferrite (Bi0.9La0.1Fe1-xGdxO3 (x = 0.01, 0.03, 0.05, 0.07, 0.1, and 0.15). Conventional solid state reaction technique was used to synthesize ceramic samples. To investigate the influence of co-substitution on the phase formation and crystal structure, X-ray diffraction method (XRD), Scanning electron microscopy (SEM) and Raman spectroscopy were utilized. Probing the structural properties by changing Gd ratio was carried out to ensure single phase of rhombohedral R3c structure. Hence, the exploration of dielectric properties of single phase modified BiFeO3 (BFO) ceramic was executed by room temperature capacitance and loss tangent measurements. It was found that by substitution of 10 mol% La for Bi and up to 5 mol% Gd for Bi, perovskite structure of rhombohedral symmetry and R3c space group were formed. This possessed enhanced magnetization and reduced dielectric loss compared to pure BFO.

Low loss and tailored high‐frequency performances of BaO‐doped NiZnCo magneto‐dielectric ferrites

AbstractSpinel ferrite ceramics of nominal composition Ni0.5Zn0.3Co0.2Fe2O4 (NiZnCo) with various BaO doping were successfully synthesized for applications as novel high‐frequency magneto‐dielectric materials. The influences of BaO doping on the crystal phase, density, microstructure, and magnetic and dielectric performances in the frequency range of 0.1 to 5 GHz were systematically studied. It is revealed that the doped Ba2+ ions aggregate to the grain‐boundary regions and lead to the formation of BaFe2O4 phase that significantly restrains the growth of NiZnCo ferrite grains. Correspondingly, permeability and permittivity are effectively tailored through the varied grain size and density, which is demonstrated by the magnetic circuit model and the modified effective medium theory proposed herein. As BaO content x = 1.2‐1.8 mol%, the NiZnCo ferrites reveal the excellent performance with almost equal values of μ′ and ε′, yielding a characteristic impedance to be nearly identical as that of free space over a wide frequency range of the VHF and UHF bands. Furthermore, the magnetic loss is effectively reduced at high frequencies, where the typical tan δμ at 0.5 GHz is decreased to ~0.043 with a reduction of up to 37% and the loss factor (tan δμ/μ′) is as low as ~0.006.

Gamma-irradiation induced modifications in structural and magnetic properties of nanocrystalline Mn0.5Zn0.5 SmxFe2-xO4 ceramics

The changes in structure, infrared absorption and magnetic property of nanocrystalline Mn0.5Zn0.5SmxFe2-xO4 (x = 0.01, 0.03 and 0.05) ceramics were studied after different doses (0, 15 and 25 kGy) of γ-irradiation. The samples were prepared by solution combustion route. We observed that up to the highest studied dose (25 kGy) of γ-irradiation all the samples retain the cubic spinel (Fd-3m) structure as of the pristine samples, however, the lattice parameter decreases. Furthermore, we observed the metastability of Sm (and Mn) atoms at the octahedral sites. By Sm3+ doping the saturation magnetization of the pristine samples decreases, but the magnetic coercivity increases drastically, indicating enhancement of magnetic anisotropy. After γ-irradiation the magnetic anisotropy vanishes completely and the sample behaves super-paramagnetically with a small variation in saturation magnetization. Our results are important to understand the behavior and stability of the magnetic hardness created by Sm3+ doping in soft magnetic Mn–Zn ferrite ceramics.

Sintering-dependent mechanical and magnetic properties of spinel cobalt ferrite (CoFe2O4) ceramics prepared via sol-gel synthesis

Despite increasing interest in cobalt ferrites as advanced ceramics, there is still much uncertainty regarding the relationship between sintering temperature and the magnetic and mechanical properties of CoFe2O4. Precursors prepared via sol-gel synthesis were treated at 750, 800, 850 and 900 °C, pressed into pellets and fired at 1150 and 1200 °C. Samples were analyzed via XRD, Raman spectroscopy, SEM, VSM and Vickers microhardness. Pure CoFe2O4 ceramics were produced from hematite-containing precursors. While magnetic parameters remained unaffected, a significant influence was observed for CoFe2O4 grain size and morphology. The highest hardness, obtained for the 1150 °C samples, was directly associated to smaller grain sizes. Mechanical behavior diverged from the classical Hall-Petch mechanism, likely due to lower grain size homogeneity. Our study achieved a thorough understanding of the magnetic and mechanical behavior of CoFe2O4 ceramics, enabling the optimized selection of processing according to the desired final properties of these materials.

Effect of ball milling on defects level, Curie point and microstructure of LiTiZn ferrite ceramics

In a present work, a comparative study of two types of LiTiZn samples of ferrite ceramics, which were sintered using conventional ceramic technology at a temperature of 1010 °C for 2 h and which were made with preliminary mechanical treatment in a ball planetary mill, was carried out. It is shown that mechanical treatment in a ball mill leads to a decrease in the defects level, an increase in the Curie point and a demagnetizing factor of ferrite ceramics. The growth of the demagnetizing factor is associated with an increase in the porosity of ferrite ceramics samples pre-grinded in ball. According to the X-ray phase analysis data, the lattice parameter and the coherent scattering region decrease in this case, and the microstrain is reduced by an order of magnitude. The defects level was assessed by the results of mathematical processing of the temperature dependences of the initial permeability using the previously proposed phenomenological expression. Measuring TG/DTG curves in a magnetic field allowed, on the one hand, to confirm a significant difference in Curie points for different types of samples, on the other hand, to detect the presence of an additional magnetic phase in ball-milled ferrite ceramics samples.

Enhancement of local piezoresponse in samarium and manganese co-doped bismuth ferrite ceramics

Field-induced polarization switching and electromechanical mechanisms in lead-free multiferroic BiFeO3 materials are essential for applications in nanoscale logic and magnetoelectric-controlled devices. This work highlights enhanced ferroelectric polarization switching and electromechanical strain behaviors in (Sm, Mn) co-doped (Bi0.95Sm0.05)(Fe1-xMnx)O3 ceramics with increasing Mn substitution. The Mn L-edge and oxygen K-edge synchrotron X-ray absorption spectra confirm a Mn3+→Mn4+ valence shift and reduced O 2p–Fe 3d and O 2p–Bi 6sp orbital hybridizations in the Mn-doped specimens. High-resolution transmission electron microscopy (TEM) confirms larger polar nano-regions (PNRs) and oxygen octahedral tilt in the Mn-doped specimens. Out-of-plane piezoresponse force microscopy (OP-PFM) shows improved local ferroelectric polarization and electromechanical response within grains by the Mn substitution. The enhanced ferroelectricity and piezoelectricity may originate from collective effects, including fewer oxygen vacancies, reduced covalent bonding, larger oxygen octahedral tilt and PNRs, caused by the Sm and Mn co-substitution.

Microstructure and enhanced magnetic properties of low-temperature sintered LiZnTiMn ferrite ceramics with Bi2O3-Al2O3 additive

Bi2O3 and Al2O3 were proven to separately have an impact on grain growth of LiZn ferrite ceramics. In this study, we synthesized LiZnTiMn ferrite ceramics under low temperature (<920 °C) using rationally designed formula of Bi2O3-Al2O3 as sintering agents. Microstructures, densities, and ferromagnetic performances were systematically investigated. Results show that appropriate amount of Bi2O3-Al2O3 leads to successful sintering of LiZnTiMn ferrites even below 900 °C. X-Ray diffraction (XRD) and scanning electron microscopy (SEM) results show that spinel structure ferrite ceramics were obtained and that the addition of Bi2O3-Al2O3 accelerated solid-state reaction. Corresponding ferromagnetic properties, including saturation induction (Bs), remanence square ratio, coercivity (Hc), ferromagnetic resonance linewidth (ΔH), and Ms, were also investigated. At 920 °C, with addition amount of x=1 wt%, we obtain excellent performance: Bs=306 mT, Br/Bs=0.849, Hc=2.34Oe, and ΔH=275 Oe. Results indicate that Bi2O3-Al2O3 is promising sintering agent for low-temperature sintering of LiZnTiMn ferrite ceramics.

Microstructure Formation of LiTiZn Ferrite Ceramics during Radiation-Thermal Sintering

The effect of intensification of the compaction rate of ferrite compacts under irradiation conditions with a high-power electron beam both in the heating regime and in the isothermal stage of sintering was established. The compaction mechanisms of the compacts are different at each of these stages. The intensification of compaction at the non-isothermal stage in radiation-thermal conditions is due to processes involving the liquid phase. The role of bismuth oxide in the compaction of the material at the isothermal stage of sintering is unessential, but its influence is significant in recrystallization processes. Under of Ivensen’s phenomenology, compaction curves are explained by the deceleration of annealing of structural defects responsible for the fluidity of the material. Dislocations are the most probable type of defects, satisfying the detected regularities.

XRD Analysis of Ferrite Ceramics with Different Heat Treatment

A comparative analysis of the structural characteristics of LiZnTi ferrites sintered at the temperature of 1280 and 1360 K was performed. The qualitative and quantitative X-ray diffraction (XRD) analysis of the samples, main phase structural analysis, and unit cell parameters were carried out using the non-standard method (Rietveld method). Diffraction patterns were recorded on an ARL X'TRA diffractometer in the CuKα1+α2 and CuKβ scanning modes.

Microstructures and magnetic properties of low temparature sintering NiCuZn ferrite ceramics for microwave applications

Polycrystalline (Ni0.2Cu0.2Zn0.6O)1.03(Fe2O3)0.97 (NiCuZn) ferrite ceramics with low ferromagnetic resonance (FMR) line width (ΔH) and high saturation magnetization (4πMs) were synthesized at low sintering temperatures by adding Bi2O3–ZnO–B2O3 (BZB) glass additives. Furthermore, phase compositions, microstructures, and magnetic properties of the low-temperature-sintered NiCuZn ferrite ceramics were systematically analyzed. First, X-ray diffraction patterns showed that BZB glass has no obvious effect on phase structure of NiCuZn ferrites. Moreover, scanning electron microscopy images revealed that BZB glass can dramatically enhance grain growth and densification of the ferrites. More importantly, due to grain growth and reduction of porosity, ΔH of the NiCuZn ferrite sintered at 870 °C decreased significantly from 521.2 Oe to 150.5 Oe. Moreover, compact and uniform NiCuZn ferrites possessed high saturation magnetization (4πMs = ~4267 Gauss), reduced coercivity (Hc = ~92.2 A/m), and large saturation flux density (Bs = ~269.1 mT). The above mentioned results indicated that low-melting point BZB glass is an optional sintering aid to promote grain growth and enhance gyromagnetic properties of NiCuZn ferrites sintered at low temperature.

Electrical and magnetic properties of ZrO2-doped lithium-titanium-zinc ferrite ceramics

Abstract This report documents the effect of 0–3 wt% ZrO2 additive on the electrical and magnetic properties of LiTiZn ferrite. Ferrite powder of Li0.65Fe1.6Ti0.5Zn0.2Mn0.05O4 composition was synthesised at 900 °C for 4 h in air. Ferrite ceramics doped with ZrO2 were sintered at 1010 °C for 2 h in air. A spreading resistance analysis showed that LiTiZn ferrites exhibited nonuniform distribution of depth DC resistivity, which varied in the range of (0.25–2.3) × 109 Ω⋅cm depending on the amount of additive. Zirconia also affected the magnetic properties of ferrite so that the magnetisation increased and the initial permeability decreased as the ZrO2 content increased. In addition, the Curie temperature varied. The permeability spectra measured in the frequency range from 10 MHz to 18 GHz changed depending on the zirconia content.

Calculation of Radiation Absorption Parameters for Some Selected Ferrite Ceramics

Ferrit seramikleri nispeten düşük maliyetli, üretilmesi kolay, mükemmel korozyon ve demanyetizasyon direnci özelliklerinden dolayı en yaygın kullanılan kalıcı mıknatıs malzemeleridir.Ferrit seramikler tıbbi cihazlarda, manyetik terapide, manyetik oyuncaklarda, hoparlörlerde, mikrofonlarda, ses sistemlerinde, kalıcı manyetik aktüatörlerde, watt-saat metrelerde, sensörlerde, ceptelefonlarında, elektrik motorlarında, vb. kullanılırlar. Bu çalışmada 1 keV ile 100 GeV enerji aralığında BaFe12O19, SrFe12O19, Y3Fe5O12, LiFeO2 için kütle soğurma katsayıları, moleküler tesirkesitleri, atomik tesir kesitleri, elektronik tesir kesitleri, etkin atom numaraları ve etkin elektron yoğunlukları incelenmiştir. Soğurma parametrelerinin değişimi fotoelektrik etki, Compton saçılması veçift oluşum süreçleriyle yorumlanmıştır.

TiO2 tailored low loss NiCuZn ferrite ceramics having equivalent permeability and permittivity for miniaturized antenna

Abstract Matching permeability and permittivity, low magnetic and dielectric loss tangent and high refractive index play a critical role in designing a miniaturized antenna with high performance. Here, TiO2 was introduced into Ni0.368Cu0.2Zn0.432Fe1.96O3.94 ferrite ceramic to adjust equivalent permeability and permittivity via suppressing grain growth. The effects of concentration of TiO2 and sintering temperature on microstructure, complex permeability and permittivity, DC resistivity, and saturation magnetization of NiCuZn ferrite ceramics were investigated. SEM results indicated that TiO2 obviously retarded grain growth to achieve uniform and dense NiCuZn ferrite ceramics with small grains (∼0.60 μm). Also, it was found that the addition of TiO2 can enhance the DC resistivity and reduce loss factors via increasing in fraction of grain boundaries. Furthermore, different sintering temperatures were chosen to control the matching permeability and permittivity and to promote densification. At last, a NiCuZn ferrite with the equivalent permeability to permittivity (μ′ = 12.90, e′ = 12.76, @ 40 MHz), very low loss factors (tanδμ = 0.050, tanδe = 0.00022, @ 40 MHz), and high DC resistivity was obtained sintered at 1000 °C when 16 wt% TiO2 was added. Thus, NiCuZn ferrite ceramics doping TiO2 show a lot of potential to be used as a substrate material in miniaturizing antenna for futuristic electronic devices.

High-performance inductive couplers based on novel Ce3+ and Co2+ ions co-doped Ni-Zn ferrites

Abstract High-performance inductive couplers require Ni-Zn ferrites of high saturation magnetization, Curie temperature, permeability and application frequency. However, for inductive couplers some of these properties run against each other in one ferrite. To balance these requirements, in this work, novel Ni-Zn ferrite ceramics co-doped by Ce3+ and Co2+ ions with chemical formula Ni0.4Zn0.5Co0.1CexFe2-xO4 (x = 0–0.06) were designed and fabricated by a molten salt method. For the acquired ferrites, both Ce3+ and Co2+ ions could come into the lattices. The initially doped Co2+ ions would cause a slightly decreased grain size and dramatically reduced the specimen densification, but the further added Ce3+ ions could effectively inhibit the density reduction, while the grain size continues to dwindle. The additional Ce3+ ions would generate a foreign CeO2 phase in the acquired specimens. The sole doping of Co2+ ions would aggrandize the saturation magnetization of ferrites, but the introduction of Ce3+ ions would cause its decrease. However, with an appropriate doping level, the Ce3+ and Co2+ ions co-doped ferrites could preserve a relatively high saturation magnetization, while the Curie temperature and cut-off frequency of the ferrites are dramatically augmented, although the permeability would be somewhat reduced. The as-acquired ferrites were simulated to apply in inductive couplers, revealing that the devices manufactured by the Ni0.4Zn0.5Co0.1CexFe2-xO4 ferrites had significantly high maximum operating frequency, compared with that of the one manufactured by pure Ni0.5Zn0.5Fe2O4 ferrite.

Estimation of phase homogeneity of LiTiZn ferrites from the temperature dependence of the initial permeability near the Curie point

The estimation of the chemical homogeneity of lithium-substituted ferrite ceramics based on an analysis of the temperature dependences of the initial permeability near the Curie point was made. The transition of ferrite from ferrimagnetic to paramagnetic state at the Curie point is sensitive to the phase and chemical homogeneity of the material. It is shown that the best homogeneity is in ferrite products of the SL-187 brand compared with samples of ferrite ceramics, sintered in the laboratory conditions.

A superior microwave absorption material: Ni2+-Zr4+ Co-Doped barium ferrite ceramics with large reflection loss and broad bandwidth

Large reflection loss and wide bandwidth are significant targets, determining the microwave absorption ability. However, it is still a challenge to simultaneously satisfy the two conditions. As a multifunctional material, BaFe12O19 possess excellent electromagnetic properties in the microwave frequency band. Due to the natural resonance phenomenon of the material, BaFe12O19 can produce a large magnetic loss which correlates with Fe3+ content, and the microwave absorption characteristics of barium ferrite can be modulated by ion doping. As a typical magnetic metal, Ni coupled with high-valence state Zr4+ doping helps to produce double resonance peaks. In this work, Ni2+-Zr4+ co-doping M-type barium ferrites (BaFe12-2xNixZrxO19, BNZFO-x, x = 0–0.8) were prepared conveniently by solid-state reaction method. Several necessary measurements to characterize its microwave absorption property have been operated such as morphology, magnetic performance and electromagnetic parameters. The results show that reflection loss and bandwidth can be simply tuned by tailoring Ni2+-Zr4+ content. The reflection loss peak drifts from 18 GHz to 9.76 GHz, which involves a half of the studied frequency range. The maximum reflection loss achieves −60.6 dB and the corresponding bandwidth over −10 dB is 7.68 GHz for BNZFO-0.6 ceramic with only 2.1 mm thickness. Thus, the doping of Ni2+-Zr4+ ion pairs is beneficial to improve the absorbing properties of the material, and the superior microwave absorption property may originate from its inner double natural resonance in micro-scale. The excellent microwave absorption properties suggest that BNZFO-x is a promising candidate applied for designing electromagnetic shielding devices.

Enhanced piezomagnetic coefficient of cobalt ferrite ceramics by Ga and Mn doping for magnetoelectric applications

The magnetic, magnetostrictive, and electrical properties of Ga- and Mn-doped cobalt ferrite are reported as a function of composition. Materials with improved functionality for magnetoelectric composites are obtained. Magnetic characterizations reveal the effectiveness of the dopants to reduce the typically high magneto-crystalline anisotropy of cobalt ferrite and significantly enhance piezomagnetic coefficients. CoGa0.15Fe1.85O4 ceramic shows large effective piezomagnetic coefficient q11, 3.9 × 10−6 kA−1 m, which is among the highest values reported for cobalt ferrite-based ceramics. Additionally, a two order of magnitude increase of resistivity is found after doping, which makes this material specially suitable for particulate composites. On the contrary, CoMn0.25Fe1.75O4 ceramic has the highest value of q11+q21 (∼1.9 × 10−6 kA−1 m), which is the relevant parameter for laminated composites. Analytical calculations of the transverse magnetoelectric coefficient α31E for bilayers containing these optimized magnetostrictive phases are also reported, and they demonstrate their high potential for developing new magnetoelectric composites.

Effects of Sm substitution on ferroelectric domains and conductivity in bismuth ferrite ceramics

The large piezoelectric coefficient and multiferroicity of bismuth ferrite (BFO) make it an attractive candidate for lead-free ferroelectric devices. However, large leakage currents have limited broader applications. Rare-earth substitutions in BFO have been shown to improve ferroelectric and magnetic properties. In this work, we employed piezoresponse and conductive atomic force microscopy to study ferroelectric domains in Bi1-xSmxFeO3 (x = 0–0.150) grown by the co-precipitation method. The combined piezoresponse and conductivity measurements can directly visualize the local ferroelectric domains under different sample bias. At Sm mol% > 7.5, Sm-substitution effectively lowers defect-generated conductivity. At Sm mol% < 7.5, conductivity increases due to conductive domain walls inside sample grains. The surfaces of these conductive samples exhibit a p-type rectifying behavior while the bulk is n-type. Our work details how the local piezoelectric properties and transport behaviors of BFO ceramics change as a function of Sm-substitution.

Magnetic properties and microstructures of a Ni-Zn ferrite ceramics co-doped with V2O5 and MnCO3

The present work investigated the effect of the addition of V2O5 and MnCO3 on the microstructure and magnetic properties of Ni-Zn ferrite ceramic samples prepared by a conventional ceramic sintering method at different temperatures. With this aim, a series of samples were prepared by varying the loadings of V2O5-MnCO3 (un-doped, 0.4–0.1 wt%, 0.1–0.4 wt%, 0.2–0.3 wt%, 0.3–0.2 wt%, and 0.5–0.1 wt%, denoted as sample 1, sample 2, sample 3, sample 4, sample 5, and sample 6, respectively). The initial permeability and power loss of the different Ni-Zn ferrites were investigated with respect to the sintering temperature. The V2O5 and MnCO3 dopants significantly improved the initial permeability and power loss characteristics of the Ni-Zn ferrite at frequencies ≥0.5 MHz. When sintered at 1100 °C, sample 2 showed a maximum initial permeability of 931.23 H/m at a frequency of 1 MHz combined with a minimum power loss of 339.2 kW/m3. Co-doping with V2O5 and MnCO3 also resulted in the sintered samples with larger average grain sizes and higher density, while the sintering temperature of Ni-Zn ferrites was significantly reduced.