Microwave Ferrite Devices Research Articles

Substitution modification mechanism of YIG ferrite with a high spin-wave linewidth via fast relaxation Dy3+ ion doping and sintering modulation

YIG ferrites are often used as nonreciprocal materials in microwave ferrite devices because of their low microwave magnetic and dielectric losses. To comply with the trend of planarization and integration of microwave systems, YIG ferrites are required to withstand higher powers. In this study, we investigated the variation in material microwave properties with material composition and microstructure. The experimental results show that doping the material with high-relaxation ions Dy3+ combined with modulating the sintering holding time can effectively improve the material’s high-power microwave signal withstanding capability, and YIG ferrite with a spin-wave line width of 18.7 Oe is obtained. In addition, when the average grain size of the material is controlled within 5 μm, the effect of the average grain size on the spin-wave linewidth is more noticeable than that of Dy3+ substitution.

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.

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.

Lowered ferromagnetic resonance linewidth and enhanced spin wave linewidth of nickel-based ferrite ceramics using hot-pressing method

Previous investigations commonly employed solid-state sintering to fabricate Ni-based ferrite ceramics to improve magnetic performance. A few researchers used the hot-pressing method to prepare Ni-based ferrites, but their porosity remained relatively high values (>2%), resulting in high ferromagnetic resonance line widths (ΔH). To date, the influence of high-temperature and high-pressure forming processes on ΔH and spin wave line width (ΔHk) in Ni-based ferrite ceramics has been rarely reported using hot pressing. This study utilized a uniaxial hot-pressing method and systematically investigated the effect of porosity, grain size and grain uniformity on the magnetic properties of Ni-based ferrite ceramics. Porosity played a crucial role in determining ΔH at different sintering temperatures. As the sintering temperature increased, the reduced porosity resulted in a decrease in ΔH. Under varying sintering pressures, the grain uniformity primarily affected ΔH. Increasing pressures led to more uniform grains, causing a decrease in ΔH. The ΔHk was directly associated with the grain sizes. With the increase of sintering temperatures, the grain sizes increased, leading to a decrease in ΔHk. Conversely, as the pressure increased, the decreased grain sizes brought the increased ΔHk. Compared to other hot-pressing results on the Ni-based ferrite ceramics, the optimized high-temperature and high-pressure processing with annealing significantly reduced the porosity of Ni-based ferrite ceramics (0.11%). In comparison with the solid-state sintering without pressures, the optimized hot-pressed Ni-based ferrite ceramics exhibited a 7% increase in saturation magnetization, a 63% reduction in ΔH and a 6.5% increase in ΔHk. The striking reduction of ΔH suggests that microwave devices assembled from Ni-based ferrite ceramics could withstand high power levels while minimizing lower electromagnetic losses, predicting promising applications for Ni-based ferrite materials in high-power microwave ferrite devices.

Effect of Mn3+ doping on the loss of Li0.37Zn0.26Ti0.12Fe2.37O4 ferrite

In this paper, a series of the gyromagnetic ferrite Li0.43Zn0.26Ti0.12MnxFe2.19−xO4 (x = 0–0.14) samples were prepared with the solid-phase reaction sintering method. The influences of Mn3+ doping on the microscopic morphology, ferromagnetic resonance linewidth, and microwave dielectric loss of LiZnTi ferrite were investigated. Doping in an appropriate amount of Mn3+ will reduce the saturation magnetization of the sample and the magnetocrystalline anisotropy of the ferrite. It also inhibited the generation of Fe2+ and reduced the porosity, to the benefit of keeping the ferromagnetic resonance linewidth (ΔH) of the material and microwave dielectric loss at a low level. The results suggested that when the doping amount of Mn3+ is 0.08, the ferromagnetic resonance linewidth of the material is 27.8 × 103 A m−1, the microwave dielectric loss tangent tanδ ε equals to 0.001, and the B-H hysteresis loop remanence ratio of the sample reaches 0.87, which is a beneficial application in lock-type microwave ferrite devices.

Microstructure and microwave magnetic properties of Low-Firing Li0.42Zn0.27Ti0.11Mn0.1Fe2.1O4 ferrite

Low firing temperature and excellent gyromagnetic properties such as high remanence square ratio and narrow ferromagnetic resonance line width are required for the application in nonreciprocal microwave ferrite devices based on low temperature cofired ceramics (LTCC) technology. In this research, Bi2O3-Li2CO3 mixture was introduced as the sintering agent to lower the sintering temperature of Li0.42Zn0.27Ti0.11Mn0.1Fe2.1O4 ferrite. The influence of Bi2O3-Li2CO3 mixture upon the phase composition, composite microstructures and gyromagnetic properties of LiZnTiMn ferrite sintered at low temperature has been investigated for LTCC integration applications. With a proper amount of Bi2O3-Li2CO3 mixture, the sintering temperature of LiZnTiMn ferrite successfully reduced to below 900°C from 1100°C without degradation of magnetic properties, meanwhile, both of saturation flux density and remanence square ratio were increased.

Low-firing Li0.42Zn0.27Ti0.11Mn0.1Fe2.1O4 ceramics modified with V2O5–ZnO–B2O3 glass addition for microwave device application

A novel V2O5–ZnO–B2O3 (VZB) glass was introduced into the Li0.42Zn0.27Ti0.11Mn0.1Fe2.1O4 (LiZnTiMn) ferrites for advancing low-temperature cofired ceramics technology and fabricating microwave ferrite devices by the multilayer process. The results reveal that the addition of VZB glass is an effective way to improve the densification, microstructure, and ferrimagnetic properties of the LiZnTiMn ferrites. The relationship among dopant amount, sintering mechanism, and structural distribution characteristic was established, tailoring the foundation of ferrimagnetic performance of low-temperature fired LiZnTiMn composites. The resulting VZB glass as flux promotes the microstructural uniformity and compactness and also provides the optimized physical properties of low-temperature sintered LiZnTiMn composites. An appropriate amount of VZB glass (~0.5 wt%) could enhance the saturation magnetization (from 52.2 to 72.3 emu/g) and remanence ratio of saturation induction (from 0.76 to 0.85) and reduce the coercivity of magnetic induction intensity (from 685 to 199 A/m) of the ferrite composites sintered at ~900 °C. Moreover, the ferromagnetic resonance linewidth of LiZnTiMn composites doped with 0.5 wt% VZB glass decreased from 860 to 195 Oe because of the combined effect of good uniformity and low porosity. Thus, with a low-temperature sintering process, the VZB glass could be a promising additive for achieving low-loss LiZnTiMn ferrite used in microwave devices.

Synthesis of Highly Uniform and Compact Lithium Zinc Ferrite Ceramics via an Efficient Low Temperature Approach.

LiZn ferrite ceramics with high saturation magnetization (4πMs) and low ferromagnetic resonance line widths (ΔH) represent a very critical class of material for microwave ferrite devices. Many existing approaches emphasize promotion of the grain growth (average size is 10-50 μm) of ferrite ceramics to improve the gyromagnetic properties at relatively low sintering temperatures. This paper describes a new strategy for obtaining uniform and compact LiZn ferrite ceramics (average grains size is ∼2 μm) with enhanced magnetic performance by suppressing grain growth in great detail. The LiZn ferrites with a formula of Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 were prepared by solid reaction routes with two new sintering strategies. Interestingly, results show that uniform, compact, and pure spinel ferrite ceramics were synthesized at a low temperature (∼850 °C) without obvious grain growth. We also find that a fast second sintering treatment (FSST) can further improve their gyromagnetic properties, such as higher 4πMs and lower ΔH. The two new strategies are facile and efficient for densification of LiZn ferrite ceramics via suppressing grain growth at low temperatures. The sintering strategy reported in this study also provides a referential experience for other ceramics, such as soft magnetism ferrite ceramics or dielectric ceramics.

Current-induced nonlinear magnetoelectric effects in strontium hexaferrite

We report on the observation of nonlinear magnetoelectric effects at room temperature due to a dc current in the ferrimagnetic $M$-type strontium hexaferrite platelets. Utilizing microwave measurement techniques and data on the shift in magnetic mode frequencies, it was found that a dc current along the hexagonal $c$ axis resulted in a significant decrease in the saturation magnetization and an increase in the uniaxial magnetocrystalline anisotropy field. These changes in the magnetic order parameters were directly proportional to the square of applied electric field and were found to be much higher than variations due to Joule heating. A phenomenological theory that takes into account the current-induced magnetobielectric (MBE) effects is proposed. Expressions for coupling coefficients for MBE effects have been obtained and have been calculated from the variations in magnetic order parameters. The electric field $E$ (or current) tuning of the magnetic modes in $\mathrm{Sr}M$ reported here is orders of magnitude stronger than strain mediated $E$ tuning of magnetic resonance in hexaferrite-ferroelectric composites. The nonlinear magnetoelectric effects in hexaferrite, therefore, open up an avenue for the realization of $E$-tunable broadband microwave and millimeter wave ferrite signal processing devices such as resonators and filters.

ChemInform Abstract: Consequences of Magnetic Anisotropy in Realizing Practical Microwave Hexaferrite Devices

AbstractReview: 26 refs.

Consequences of magnetic anisotropy in realizing practical microwave hexaferrite devices

With the rapidly growing demand for bandwidth in wireless communication systems and increasing frequencies of operation of electronic devices, in recent years resurgence in scientific interest in highly anisotropic hexagonal ferrites has been noted. This interest stems in part from a number of emerging applications that pose significant materials challenges that cannot be addressed using traditional rf and microwave ferrite materials. In this manuscript, several specific applications that could benefit from the unique properties of hexagonal ferrites are discussed. Fundamental principles of operation, materials requirements, as well as unique device design and modeling challenges are reviewed. Applications of textured magnetically uniaxial hexagonal ferrite composites in microwave and mm-wave non-reciprocal ferrite control devices are discussed. Applications of textured magnetically planar hexagonal ferrite composites as antenna and electronic bandgap metamaterial substrates, rf inductors and transformers, and electromagnetic interference suppression devices are reviewed. Suggestions on directions for future research and development are provided.

Long-term stability of yttrium–iron garnet films under irradiation by neutrons, protons, deuterons and electrons

Oscillations and waves of magnetization in YIG ferrite films have interesting and useful properties such as a high Q-factor, a wide variety of dispersion laws dependent on the orientation of bias magnetic fields, and a possibility to tune their frequencies in the range of several GHz by changing the magnitude of bias magnetic fields. At the same time, YIG ferrite films are widely used in different electronic devices and equipment that have already found a variety of both space and nuclear applications. So radiation stability investigations of such materials became very important. Ferrite YIG films were irradiated by reactor neutrons, 3 MeV protons and deuterons, and electrons with the energy up to 20 MeV to the fluences 1.8×10 19 n/cm 2, 9.6×10 15 p/cm 2, 1.1×10 16 d/cm 2 and 6.6×10 17 e/cm 2, respectively. The radiation effects have been analyzed using the ferromagnetic resonance method. The results of such radiation stability study show clearly that ferrite YIG films, just as devices and equipment based on them, have a long operation life and very high radiation stability. At the same time, parameters and properties of YIG films and microwave ferrite devices that use such films can be changed controllably and, moreover, more reliably than using the traditional grinding.

Nonlinear Ferrite Film Microwave Signal Processing for Advanced Communications—Physics and Devices

Microwave ferrite devices, including circulators, isolators, and phase shifters, have played a crucial role in the development of radar and other microwave signal processing applications. Recent work has advanced the basic understanding and applications for a wide range of new nonlinear spin wave phenomena in ferrite films. With the help of feedback and parametric pumping interactions, these spin wave phenomena can serve as the basis for phase locked frequency comb generators, wideband chaotic microwave oscillators, and microwave pulse multiplexers, among other devices.

Microwave characterization of magnetic thin films

An issue of current research is the integration of microwave ferrite devices with semiconductor technologies by using vacuum deposition techniques. Thin magnetic films may be used in commercial products and they can be more easily involved in the development of magnetic devices if we are able to extract their magnetic properties. One of the interesting points of this paper is to highlight the properties of a thin film, such as anisotropic behavior to release non reciprocal devices. A study of physicochemical and magnetic properties is tackled and experimental results are discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ferromagnetic resonance spectra of thick yttrium–iron–garnet films

Due to the finite aspect ratio of the ferrite, the distribution of the internal field in small planar microwave ferrite devices is strongly inhomogeneous. This is a source of additional losses through magnetostatic modes. To study the magnetostatic modes, the thickness dependence of the ferromagnetic resonance spectra was measured for a series of 2 mm square single crystal yttrium–iron–garnet films in the 35&amp;lt;h&amp;lt;220 μm thickness range. The in-plane resonance field Hr increases with thickness by 150 G, while Hr normal to film plane decreases. The uniform mode linewidth, dHr is in the 2–20 G range. A large number of magnetostatic wave modes modes is excited, covering the “full spectral width,” DH, increasing with thickness from 400 to 960 G. In a ferrite device DH has to be taken into account, giving rise to large losses in spite of the small intrinsic linewidth dHr of the material.

Ferrites for Tunable RF and Microwave Devices

AbstractMicrowave systems for communications and radar require control of propagation of the rf signal. Devices that accomplish this function include phase shifters, isolators and circulators, and tunable filters. In many instances, these devices are magnetic and are based on the variable permeability of electrically insulating ferrimagnetic oxides (ferrites). Recent advances in microwave ferrite devices have featured superconductor circuitry that promises to virtually eliminate insertion losses due to rf surface resistance. Lower conduction losses allow the use of small lightweight microstrip configurations in place of traditional bulky waveguide structures. For operation at cryogenic temperatures ferrimagnetic spinels and garnets will require chemical alteration to realize the full potential of these devices. Challenges include the reduction of magnetocrystalline anisotropy to optimize switching energies and speeds, and the elimination of fast-relaxing impurities in the magnetic garnets that can increase magnetic losses and degrade resonator Q factors at low temperatures.

Microwave Ferrite Devices

Ferrite based components are essential and critical elements in microwave systems. The seemingly mundane technology of these components finds widespread application in the form of phase shifters, circulators, magnetostatic wave devices, etc. The article reviews briefly the developments in the field of microwave ferrite devices. The progress, application and current levels of performance are discussed. Achievements in this field particularly in phase shifter development in our country are also highlighted.

Properties of ferrites at low temperatures (invited)

At cryogenic temperatures magnetic properties of ferrites change significantly from their values at room temperature, which has been the main regime for most device applications. Recently, microwave ferrite devices with superconducting microstrip circuits have been demonstrated at a temperature of 77 K with virtually no electrical conduction losses. Conventional ferrimagnetic garnet and spinel compositions, however, are not generally optimized for low temperatures and may require chemical redesign if the full potential of these devices is to be realized. Saturation magnetizations increase according to the Brillouin–Weiss function dependence that is characteristic of all ferromagnetic materials. Increased magnetocrystalline anisotropy and magnetostriction can have large effects on hysteresis loop squareness and coercive fields that are essential for stable phase shift and efficient switching. Rare-earth impurities and other ions with short spin-lattice relaxation times can cause increased microwave losses. In this article, the basic magnetochemistry pertaining to ferrites will be examined for adaptation of ferrite technology to cryogenic environments.

Progress of research on magnetism in China

In this paper, a comprehensive review of the research on magnetism in China has been made by dividing it into seven aspects, which are: (1) permanent magnetic material; (2) soft magnetic material; (3) magnetic storage material; (4) microwave ferrite material and devices; (5) magnetic recording; (6) amorphous magnetic material and (7) magnetic theory. The process of historical changes and development in each aspect and the significant results achieved during the corresponding period have been given in detail. In addition, the modern level of the study on magnetism in China and its important contributions to the development of magnetism all over the world have also been introduced.

Analysis of microwave ferrite devices by using the finite-element method

In this paper, we describe a numerical approach for solving the problem of H-plane waveguide junctions containing lossy ferrite posts of arbitrary shape. This approach is based upon the use of triangular finite elements and employs a local type of radiation-boundary condition on the waveguide ports to truncate the original domain, which is infinite, into a finite and manageable size region.