Gyromagnetic Properties Research Articles

Improved gyromagnetic properties of LiZnTi ferrites co-fired with Bi2O3-La2O3 additives at low temperature

In this work, low temperature-sintered Li0.43Zn0.27Ti0.13Fe2.17O4 ferrites mixed with x wt.% (x = 0.00–0.30 wt%) of La2O3 and 1.5 wt% of Bi2O3 were successfully prepared by the solid-state reaction method. The variations in phase composition, microstructure, and gyromagnetic properties of the as-prepared samples were studied in detail. XRD patterns and refinement results show that La2O3 didn't affect the formation of the spinel phase, but a small amount of La3+ might enter into the lattice structure. The micro-morphological analysis and grain size statistics demonstrate that the addition of La2O3 significantly suppressed the grain growth, and the average grain size decreased from 2.19 μm (x = 0.00 wt%) to 1.14 μm (x = 0.15 wt%). The uniformity of the grain size distribution was improved, and the degree of densification was significantly increased. Meanwhile, the saturation magnetization (4πMs) increased from 3921 Gs to 3989 Gs, the coercivity (Hc) decreased from 457.5 A/m to 312.5 A/m, and the ferromagnetic resonance linewidth (ΔH) decreased from 328.5 Oe to 220.7 Oe. Our study indicates that the Bi2O3-La2O3 mixture is an effective sintering additive for low-temperature sintering of LiZnTi ferrite ceramics, which will play an important role in the development of low-temperature co-fired ferrites.

Phase formation, microstructure and gyromagnetic properties of c-axis oriented M-type hexaferrite applied to self-biased circulator

Self-biased structure based on hexaferrite demonstrates potential for achieving planar miniaturization of microwave circulator. Appropriate magnetocrystalline anisotropy field Ha and high squareness ratio Mr/Ms are indispensable for hexaferrite to meet with specific operating frequency and reduce loss of circulator, respectively. Gd3+-Mg2+ co-substitution is introduced to adjust Ha of M-type hexaferrite Sr1-xGdxFe12-xMgxO19 (SrM, x= 0.00, 0.05, 0.10, 0.15, 0.20, 0.25) while maintaining valence equilibrium. A Mr/Ms as high as 0.88 is achieved through ceramic process combined with magnetic field orientation. The ferromagnetic resonance linewidth of 774 Oe is detected by perturbational method based on coplanar waveguide at 43 GHz. Finally, A self-biased circulator using slotted structure based on SrM is designed, showcasing effective circular transmission functionality at Ku band.

Ku-band 300 kW high power ferrite phase shifter.

Phase shifter (PS) is a key component of a phased array antenna (PAA) system, which controls the microwave phase and realizes the antenna beam forming and scanning. A ferrite PS (FPS) is a current-controlled PS that uses the ferrite's gyromagnetic properties to realize phase shifting. It has the advantages of short phase switching time, low microwave loss, and high reliability and, therefore, has been widely used in low-power PAA systems. However, the power handling capability of the traditional Ku-band FPS is only a few kW, prohibiting FPS from being used in high-power microwave (HPM) PAA systems. Spurred by this concern, this paper proposes a new dual-toroid FPS structure with an external magnetic excitation. By optimizing the PS configuration, improving the integration process, and enhancing the performance of ferrite materials, a single FPS in the Ku band has reached the power handling capability of more than 300 kW with an insertion loss of less than -1.2 dB, the phase shift range of 0°-360°, the width less than 11.5mm, and the ability of a one-dimensional array. The FPS has the potential to be used in the PAA of an HPM system, laying a foundation for the research of the HPM PAA system.

Magnetic and dielectric properties of Mn2+ and Nb5+-doped NiCuZn ferrites for K-band junction circulators

Ni0.42-x/3Nbx/3Cu0.18Zn0.4MnxFe1.98−xO4−δ (x = 0–0.1) materials, possessing a high saturation magnetization, high dielectric constant, and narrow ferromagnetic resonance linewidth, were prepared via the solid-phase reaction method. The cation distribution, as well as the dielectric and gyromagnetic properties, were studied in detail. Mn2+ and Nb5+ incorporated in the lattice occupy tetrahedral site, causing the redistribution of cation and the reduction of A–B superexchange interaction. This leads to an increase in saturation magnetization followed by a decrease. The introduction of appropriate amounts of Mn2+ and Nb5+ ions reduces the magnetocrystalline anisotropy constant |K1| and thus reduces the ferromagnetic resonance linewidth (ΔH). Furthermore, high polarisability of Mn2+ and Nb5+ causes the increase in the dielectric constant of the ferrites. At x = 0.08, excellent gyromagnetic and dielectric properties, including a high dielectric constant (ε’ = 15.4@100 MHz), high saturation magnetization (4πMs = 4577 G), and narrow ferromagnetic resonance linewidth (ΔH = 129 Oe@9.55 GHz) for the NiCuZn ferrite, was achieved. Finally, a K-band microstrip circulator operating at 20.8 to 28 GHz was designed. The simulation showed that the isolation of the circulator in the working frequency band is greater than 20 dB, showing the potential of the prepared ferrites in microwave circulators.

Synthesis and gyromagnetic properties of highly-dense LiZnTi ferrite for microwave ferrite devices

LiZnTi ferrites with dense microstructure and excellent gyromagnetic properties are a critical class of materials for microwave ferrite devices. Many reported studies have demonstrated that grain refinement and good gyromagnetic properties is often contradictory. In this work, we have successfully prepared a highly-dense LiZnTi ferrite with small average grain size (<1.0μm) and good gyromagnetic properties by hot-pressure sintering (HPS) method. Interestingly, SEM images revealed that the hot-pressure sintering with zero holding time not only promoted densification of the LiZnTi ferrites, but also can realize their grain refinement, which effectively reduced porosity and improved gyromagnetic properties. Meanwhile, we found that the average grains size (GSave.) of the HPS950 sample is smaller than the TS950 and HPS900 samples due to the synergistic effect of applied pressure (zero holding time) and Bi2O3 liquid phase. Finally, a LiZnTi ferrite with uniform, dense grains (GSave. = 0.85 μm and ρr = 98.1 %) and good gyromagnetic properties (4πMs = 3859.6Gs and ΔH = 287.4 Oe) was obtained by hot-pressure sintering at ∼950 °C.

Zn-Ti co-substituted LiZn microwave ferrites: Sintering characteristics and gyromagnetic properties

To meet the low-loss and high-frequency application requirements of modern electronic information systems for integrated microwave devices, Zn-Ti co-substituted LiZn microwave ferrites were prepared in this work. The results demonstrated that Zn-Ti co-substitution promoted the grain growth and densification process during sintering, leading to a decrease in the pore-induced linewidth (ΔHp) of LiZn composite microwave ferrites; the introduction of non-magnetic Zn2+ and Ti4+ ions lowered the content of Fe3+ ions in the ferrites, which reduced the magnetocrystalline anisotropy constant |K1| and thus diminished the anisotropy-induced linewidth (ΔHa). Besides, the dielectric loss of the material decreased with increasing Zn-Ti substitution amounts (x) due to the reduction of Fe2+ ion content. As a result, when x = 0.35, the FMR linewidth was decreased from ∼251 Oe to ∼97 Oe, and the dielectric loss was greatly reduced from >100×10−4 to ∼3.82×10−4 in the ferrites. The material also exhibited excellent properties including high saturation magnetization (∼3913 Gauss), high Curie temperature (∼304 °C), and low coercivity (∼2.05 Oe).

Control of sintering characteristics and gyromagnetic properties of LiZn-based microwave ferrite ceramics by Nb2O5 doping

In this study, a new strategy of trace amounts of Nb2O5 doping was employed to control microwave loss of Ti-Mn-Bi co-substituted LiZn-based ferrite ceramics sintered at 890 °C. The results revealed the distribution of doped Nb in the spinel ferrites. Partial Nb5+ ions entered the lattices and induced the generation of Fe2+ ions, resulting in a decrease in the magnetocrystalline anisotropy linewidth (ΔHa). The rest of Nb2O5 remained at grain boundaries and formed high resistance layers, which contributed to lowering the dielectric loss (tanδε). Due to the particular distribution of Nb, a dual-structure and higher densification were observed, and thus the porosity-induced line broadening contributions (ΔHp) was reduced. Notably, by doping with 0.15 wt.% Nb2O5, the LiZn-based ferrites presented excellent magnetic properties (ΔH = 87 Oe, tanδε = 3.24 × 10-4, 4πMs = 3799 Gauss, Br/Bs = 0.9), which shows promising potential for low-loss microwave ferrite devices.

Phase composition, microstructure, and gyromagnetic properties of LiZnTi ferrites sintered at low temperature

In this study, a series of Li0.43Zn0.27Ti0.13Fe2.17O4 ferrites were successfully synthesized by solid-state reaction method at 920 ℃ employing low melting point V2O5 as sintering aid. The X-ray diffraction (XRD) studies demonstrated that all samples exhibited spinel phase. Microscopic image analysis revealed that both the grain growth and uniformity were significantly promoted. The average grain size was increased from 0.65 µm to 4.53 µm when V2O5 was increased from 0.0 wt% to 2.4 wt%. In terms of the magnetic properties, the saturation magnetization (4πMs) of the samples increased from 2915 Gs to 3434 Gs, the coercivity (Hc) decreased from 848.3 A/m to 242.2 A/m, and the ferromagnetic resonance linewidth (ΔH) decreased from 963 Oe to 543 Oe. It could be noted that the proper addition of V2O5 is the key to optimizing the microstructure and magnetic properties of LiZnTi microwave ferrite. Therefore, as an effective additive, V2O5 can promote the development of low temperature co-fired ferrites.

Effect of Bi2O3-CuO Flux on the Microstructure, Soft Magnetic Properties, and Gyromagnetic Properties of NiCuZn Ferrites for LTCC Devices.

In this work, the electromagnetic properties of Ni0.22Cu0.31Zn0.47Fe2O4 (NiCuZn) ferrites doped with 0.3 wt% Bi2O3 + xCuO flux (x = 0.2, 0.4, 0.6, and 0.8 wt%) were studied. Doping resulted in a reduction in the sintering temperature to 900 °C. The doped ferrites were synthesized via the solid-state method. XRD patterns revealed that the prepared ferrites had a cubic spinel structure; thus, a moderate addition of flux did not change the crystal structure. The SEM images, as well as the density and grain size distribution of the samples, showed that the NiCuZn ferrites had densified, homogenized, and contained fully grown grains for x = 0.6 wt%. The sample exhibited good soft magnetic properties, with μ' reaching the maximum value of 245.4 for x = 0.6 wt% and ε', Ms, and Hc reaching the maximum values of 23.1, 28.06 emu/g, and 45.86 Oe for x = 0.8 wt%, respectively. Furthermore, the ferrites exhibited good gyromagnetic properties, with 4πMs reaching the maximum value of 1744 Gauss for x = 0.8 wt% and ΔH reaching the minimum value of 228 Oe for x = 0.6 wt%. NiCuZn ferrites were successfully sintered at a lower temperature (900 °C) by adding Bi2O3-CuO flux through LTCC technology and exhibited good soft magnetic properties and gyromagnetic properties. We envisage that these ferrites could be used in multilayer devices.

Cd2+-enhanced the structure, electrical and magnetic properties of low-temperature sintered NiCuZn ferrites

Ferrite materials are urgently demanded in high-frequency miniaturized power electronics for their high electromagnetic properties and high electrical resistivity. However, traditional NiZn ferrites are faced with low resistivity and high loss at low-temperature sintering, which severely restrict their applications. In this study, CdO was substituted into Ni0.22Cu0.2Zn0.58Fe2O4 ferrites at a presintered stage to refine the grain size and to achieve superior performance at low-temperature sintering. Interestingly, the electrical, magnetic and gyromagnetic properties of the NiCuZn ferrites exhibited a strong dependence on the concentration of Cd2+ ions. The Cd2+ ions entered into the lattice and substituted for Fe3+ at the octahedral site. SEM image results showed that CdO-substituted NiCuZn ferrites for the first sintering stage possess inhibition of abnormal grain growth, which can effectively solve the problem of shrinkage and grain compaction of ferrite materials in LTCC technology. Furthermore, to promote the grain growth at low sintering temperature, the optimized Bi2O3 additives were added at final sintering stage. The resistivity of the optimized Cd2+ ions is significantly enhanced from 2.41 × 108 Ω cm to 8.51 × 108 Ω cm. Finally, the NiCuZnCd (x = 0.15)-1.2 wt% Bi2O3 ferrites with the highest densification possess ρ = 8.51 × 108 Ω cm, ε′ = 18, tan δε = 6.0 × 10−3, μ′ = 81, fr = 117 MHz, tan δμ = 4.8 × 10−2 and ΔH = 281 Oe. This work provides a new doping method for the design of the high frequency LTCC device.

Gyromagnetic properties of Cu-substituted NiZn ferrites for millimeter-wave applications

In this work, NiCuZn ferrites with different CuO contents were prepared by solid-state method. The influences of the divalent Cu2+ on the crystal structure, microstructure and magnetic properties of NiCuZn ferrite were studied in detail. X-ray diffraction characterization showed that Cu2+ may either replace Ni2+ and enter into crystal lattice, or distributed at grain boundaries in the form of compound. SEM results showed that adding appropriate amount of CuO can promote grain growth and prepare dense NiCuZn ferrites. Especially, the density of the ferrite sample reaches its maximum value of 5.23 g/cm3 when the amount of CuO is 0.20. However, superfluous Cu2+ exists in the form of liquid phase at local grain boundaries once the content of Cu2+ reached 0.25. Moreover, the magnetic hysteresis loops revealed that the specific saturation magnetization first increased and then decreased and the highest value of 76.6 emu/g was obtained at x = 0.10. Consequently, a NiCuZn ferrite with an appropriate microstructure and with high density (5.16 g/cm3), high saturation magnetization (76.0 emu/g), low ferromagnetic resonance (FMR) linewidth (160 Oe) and 4πMs (4930 G) could be obtained at a Cu content of x = 0.15.

Research on performance of piezoelectric superimposed beam energy harvester under gyromagnetic excitation

In this paper, In order to make use of the rotating motion characteristics of the roller cage shoe structure in vertical shaft lifting guide device, a nonlinear gyromagnetic excitation piezoelectric superposition beam energy harvester with compact structure, non-contact and high energy harvester efficiency is designed. The nonlinear force between moving magnet and stationary magnet is used to transform the rotating motion of the roller cage shoe into the end vibration of the piezoelectric vibrator. In order to improve the utilization rate of the piezoelectric plate and the low-amplitude response sensitivity of the energy harvester, acrylic material is introduced to re-place the traditional metal substrate, the bottom piezoelectric vibrator is hinged with the end of the top piezoelectric vibrator, and the middle part of the piezoelectric vibrator ends are longitudinal-superimposed beam structure with chute connection. The structural parameters, gyromagnetic excitation properties and strength of the piezoelectric vibrator are optimized and analyzed through finite element simulation and experiments, and the longitudinal and transverse arrays of piezoelectric vibrators are designed. The effects of terminal connection mode, array spacing, array number and load resistance on the power generation performance of the energy harvester are investigated. The results show that when the number of vertical arrays is 8 layers and the array spacing is 1.5 mm, higher voltage output and vibration consistency are achieved. When the horizontal array is 7 groups and the load is 10 kΩ, the maximum output power of the energy harvester is 11.26 mW, which can realize the self-power supply to the wireless transmitting node.

Microstructure and gyromagnetic properties of low-sintered LiZnTi ferrite doped with nano-LiZn and V2O5 additives

In this study, nanoparticles of LiZn ferrite (nano-LiZn, 0.0–10.0 wt. %) fabricated via the sol-gel method and V2O5 particles were added into a Li0.43Zn0.27Ti0.13Fe2.17O4 (LiZnTi) ferrite to realize low temperature sintering. The effects of the nano-LiZn ferrite addition on the crystalline phase formation, microstructure, and magnetic properties of LiZnTi ferrite were systematically investigated. X-ray diffraction results reveal that the LiZnTi ferrite doped with nano-LiZn and V2O5 additives present a pure spinel structure, which can be explained by liquid phase of V2O5 and spinel structure of nano-LiZn, as revealed by high-resolution transmission electron microscopy and selected area electron diffraction data. Scanning electron microscopy images show that the addition of nano-LiZn leads to a change in the microstructure, with the grains becoming uniform and dense. Additionally, the variation in the saturation magnetization (Ms) depends on the LiZn content. In particular, Ms increases with increasing LiZn content from 2.0 to 10.0 wt. %. Finally, the LiZnTi ferrite doped 4.0 wt. % nano-LiZn and 0.60 wt. % V2O5 possesses a narrow ferromagnetic resonance linewidth of 197 Oe, a reduced coercivity of 192.6 A/m, and an improved bulk density of 4.73 g/cm3.

Microstructure and gyromagnetic properties of low-sintered M-type barium hexagonal ferrite with various Ga3+ ions substitutions

The adjustment of crystal structures and properties by ion substitution has received increasing interest in recent years to solve issues related to the preparation of LTCC microwave devices. In this work, Fe3+ ions were substituted in BaFe12O19 sintered at a low temperature (920 °C). The changes in microstructures, dielectric characteristics, and magnetic properties were all examined. The ferromagnetic resonance linewidth (ΔH) of BaM ferrite was measured at magnetic fields from 6000 to 24,000 Oe. The results revealed well-grown microstructures of BaM ferrite grains at 920 °C to form typical hexagonal structures. The increase in substitution of Ga3+ ions decreased the lattice constant and cell volume of the crystals. More interestingly, the dielectric and magnetic properties depicted significant changes in the original dielectric and magnetic parameters of BaM after the substitution of Ga3+ ions. The permittivity (ε′) rose to a maximum of 16.36 at x = 0.4, while the dielectric loss angle tangent (tan δε) declined to 1.2 × 10^−3. As Ga3+ ions rose, the saturation magnetization 4πMs decreased from 3168.58 Gauss to 2571.18 Gauss. The remanence (Mr) reached a maximum value of 31.07 emu/g at x = 0.4. The ferromagnetic resonance linewidth (ΔH) of BaM ferrite sample at 31 GHz attained a minimum value of 4216.336 Oe at x = 0.8. In sum, these findings look promising for future fabrication of LTCC microwave RF devices.

Crystallographically Textured and Magnetic LaCu-Substituted Ba-Hexaferrite with Excellent Gyromagnetic Properties

Excellent gyromagnetic properties of textured, bulk Ba-hexaferrite samples are required for low-loss, self-biased applications for microwave and millimeter-wave (MMW) devices. However, conventionally processed bulk Ba-hexaferrite ceramics typically demonstrate low remanent magnetization values, 4πMr, of 2.0~3.0 kG, and relatively large ferromagnetic resonance (FMR) linewidths, ΔHFMR, of 0.8~2 kOe. These properties lead to the development of high-performance, practical devices. Herein, crystallographically textured Ba-hexaferrite samples, of the composition Ba0.8La0.2Fe11.8Cu0.2O19, having excellent functional properties, are proposed. These materials exhibit strong anisotropy fields, Ha, of ~14.6 kOe, high remanent magnetization, 4πMr, of 3.96 kGs, and a low ΔHFMR of 401 Oe at zero-bias field at the Q-band. Concomitantly, the broadband millimeter-wave transmittance was utilized to determine the complex permeability, μ*, and permittivity, ε*, of textured hexaferrites. Based on Schlöemann's theory of complex permeability, μ*, the remanent magnetization, 4πMr, anisotropy field, Ha, and effective linewidth, ΔHeff, were estimated; these values agree well with measured values.

Enhanced gyromagnetic properties of Cu-substituted LiZnTi ferrites for LTCC applications

In this work, we prepared a type of LiZnTiCu ferrite with a large grain size and enhanced magnetic properties at ∼900 °C by substituting Cu2+ ions and doping LBSCA glass. Rietveld refinement of XRD patterns indicates that the Fe3+ ions in B sites are partially replaced by the Cu2+ ions, which causes the monotone increase of lattice constant. SEM results show that the interaction of CuO nanoparticles and LBSCA glass causes two changes in the grain growth of the LiZnTiCu ferrites. The grain growth is suppressed when the amount of CuO nanoparticles is less than a threshold value (x = 0.05 for 900 °C; x = 0.20 for 875 °C). However, when enough CuO nanoparticles are added, the ferrites possess a large and compact microstructure. The variation of magnetic hysteresis (M-H) loops confirms that Ms follows the Néel's collinear spinel model with the increasing number of CuO nanoparticles (x ≤ 0.25). Finally, a type of LiZnTiCu ferrite (x = 0.15) with uniform large grains (average size >10 μm) and good magnetic parameters (4πMs = 3457.59 G, Hc = 224.4 A/m and Bs = 236.4 mT) is obtained at ∼900 °C.

Observation of optical gyromagnetic properties in a magneto-plasmonic metamaterial

Metamaterials with artificial optical properties have attracted significant research interest. In particular, artificial magnetic resonances with non-unity permeability tensor at optical frequencies in metamaterials have been reported. However, only non-unity diagonal elements of the permeability tensor have been demonstrated to date. A gyromagnetic permeability tensor with non-zero off-diagonal elements has not been observed at the optical frequencies. Here we report the observation of gyromagnetic properties in the near-infrared wavelength range in a magneto-plasmonic metamaterial. The non-zero off-diagonal permeability tensor element causes the transverse magneto-optical Kerr effect under s-polarized incidence that otherwise vanishes if the permeability tensor is not gyromagnetic. By retrieving the permeability tensor elements from reflection, transmission, and transverse magneto-optical Kerr effect spectra, we show that the effective off-diagonal permeability tensor elements reach 10−3 level at the resonance wavelength (~900 nm) of the split-ring resonators, which is at least two orders of magnitude higher than magneto-optical materials at the same wavelength. The artificial gyromagnetic permeability is attributed to the change in the local electric field direction modulated by the split-ring resonators. Our study demonstrates the possibility of engineering the permeability and permittivity tensors in metamaterials at arbitrary frequencies, thereby promising a variety of applications of next-generation nonreciprocal photonic devices, magneto-plasmonic sensors, and active metamaterials.

Nb5+ ion substitution assisted the magnetic and gyromagnetic properties of NiCuZn ferrite for high frequency LTCC devices

Nowadays, developing nickle zinc ferrites with excellent magnetic and gyromagnetic properties are of great importance for solving the matching problem of 5G communication system. However, much is discussed about soft magnetic properties, but little is reported gyromagnetic properties that is critical for microwave device applications. Herein, Nb5+ ions substituted Ni0.29Cu0.18Zn0.53NbxFe2-xO4 (x = 0.00-0.05), possessing high saturation magnetization, approriate initial permeability, high cut-off frequency and low ferromagnetic resonance linewidth (@9.55 GHz), were synthesized by low-temperature firing (900 °C). The phase structure and morphology evolutions were studied in detail. The results of morphology observations revealed that Nb5+ substitution has significant role in determining produce compact and uniform microstructures of NiCuZn ferrites via suppress the grain growth, which further corresponding enhance the magnetic and gyromagnetic properties. As a result, a uniform and compact grain size can be obtained, corresponding to the change of magnetic and gyromagenetic properties have different trends. Enhanced magnetic and gyromagnetic performance including high initial permeability (μ' = 203 @1 MHz), saturation magnetization (4πMs = 3966 Gauss) and low ferromagnetic resonance linewidth (ΔH = 203 Oe) of the NiCuZn ferrites is achieved though adjusting Nb5+ ions substitution. More importantly, this work not only for low temperature co-fired ceramic (LTCC) technology but also for high frequency and microwave frequency devices including phase shifter and radars.

Soft magnetic, gyromagnetic, and microstructural properties of BBSZ-Nb2O5 doped NiCuZn ferrites for LTCC applications

The development of 5G technology places higher performance requirements on low-temperature co-fired ceramic (LTCC) materials. Here, a solid phase method was used to prepare BBSZ-Nb2O5 doped Ni0.22Cu0.31Zn0.47Fe2O4 samples, and the effects of doping 0.3 wt% BBSZ and different contents of Nb2O5 (x = 0.1, 0.3, 0.5, 0.7, 0.9 and 1.1 wt%) on the microstructure as well as the soft magnetic and gyromagnetic properties of the resulting samples were studied. The doping with Nb2O5 promoted crystal lattice expansion and densification under low temperature sintering conditions. The sample containing an Nb2O5 content of x = 0.9 had the highest measured μ′ value of 212.6, which had increased by 15.9% relative to x = 0.1. Moreover, the measured Ms was the maximum value of 32.61 emu/g and ΔH reached the minimum value of 280 Oe for the x = 0.9 sample, which were 25.5% higher and 32.0% lower than those measured for the x = 0.1 sample, respectively. At x = 1.1, ε′ had the minimum value of 21.4, which was 21.6% lower, and Hc reached the maximum value of 30.8 Oe, which increased by 7.6%. This reduction in ΔH for the doped NiCuZn samples makes them promising materials for use in microwave gyromagnetic devices or as antenna substrates based on LTCC integration technology.

Enhancement of magnetic and dielectric properties of low temperature sintered NiCuZn ferrite by Bi2O3–CuO additives

With a series of 1.0 wt%Bi2O3–x wt% CuO (x = 0.0, 0.2, 0.4, 0.6, and 0.8) serving as sintering additives, Ni0.23Cu0.32Zn0.45Fe2O4 ferrites are successfully synthesized at a low temperature (900 °C) by using the solid state reaction method. The effects of the additives on the phase formation, magnetic and dielectric properties as well as the structural and gyromagnetic properties are investigated. The x-ray diffraction (XRD) results indicate that the added Bi2O3–CuO can lower the synthesis temperature significantly without the appearing of the second phase. The scanning electron microscope (SEM) images confirm that Bi2O3 is an important factor that determines the sintering behaviors, while CuO affects the grain size and densification. With CuO content x = 0.4 or 0.6, the sample shows high saturation magnetization, low coercivity, high real part of magnetic permeability, dielectric permittivity, and small ferromagnetic resonance linewidth (ΔH). The NiCuZn ferrites are a promising new generation of high-performance microwave devices, such as phase shifters and isolators.