Low Magnetic Loss Research Articles

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.

In-situ synthesis and magnetic properties of core-shell structured Fe/Fe3O4 composites

Abstract Fe/Fe3O4 core-shell structure soft magnetic composites were synthesized by in-situ oxidation method, the shell thickness control method and its effect on magnetic properties was investigated. The formation of Fe3O4 shell will decrease eddy-current loss for its high resistivity but reduce the permeability and saturation magnetization for its ferrimagnetic characteristics, appropriate shell thickness is the key factor to obtain a good performance of composites. The magnetic loss decreased dramatically due to the existence of a dense insulation layer and increased slightly owing to the presence of cracks in the insulation layer with the shell thickness increase further. The optimum magnetic properties of the composites were obtained for the composites with about 0.17 μm shell thickness, which exhibits a high permeability (μ) of 55, a high magnetization of 232.1 emu/g at 1 T and a low magnetic loss (W) of 30.56 w/kg at 20 mT and 100 kHz.

Influence of microstructure on magnetic and dielectric performance of Bi2O3-doped Mg Cd ferrites for high frequency antennas

Abstract The effects of microstructure on the magnetic and dielectric properties of Mg0.6Cd0.4Co0.05Fe1.95O4 spinel ferrites with the addition of 2.5 wt% Bi2O3 are investigated mainly for high frequency applications. The measurement results reveal that composites processed via low temperature co-fired ceramic (LTCC) technology at different sintering temperatures (900 °C, 920 °C, 930 °C, and 940 °C) possess excellent equivalent permeability (μ′) and permittivity (e′) (at 940 °C, μ′≈e′≈25), over a long frequency range from 1 to 100 MHz. The results also indicate that densification sintering results in ultra low dielectric loss tanδe and magnetic loss tanδμ (tanδe≈0.003, tanδμ≈0.035). In addition, the samples present enhanced magnetic properties, such as high saturation magnetization (approximately 37.94 emu/g) and appropriate coercivity (approximately 60.5 Oe) at 940 °C. This research presents the prospect of wide application of Mg Cd ferrites in high frequency applications.

Synergistic influence of micropore architecture and TiO2 coating on the microwave absorption properties of Co nanoparticles

Microporous Co@TiO2 nanoparticles (NPs) have been synthesized by combining chemical de-alloying and sol–gel strategies. The NPs with a mean size of 30 nm display a TiO2 shell of 5 nm in thickness and possess micropores in a range from 0.4 to 0.8 nm. The saturation magnetization (MS) and coercivity (HC) of the NPs are 18.6 emu/g and 337.4 Oe, respectively. The microwave absorption properties of the microporous Co@TiO2 NPs mixed with paraffin were investigated in the range of 2–18 GHz. Due to the relatively high dielectric loss tangent value and low magnetic loss tangent value, the impedance matching of the composite is better than the nonporous counterpart. The composite shows a minimum reflection loss (RL) of − 16.6 dB at a thickness of merely 2.2 mm, and the absorption bandwidth for RL ≤ − 10 dB is as large as 5.0 GHz. At a thickness of 1.9 mm, the maximum absorption bandwidth for RL ≤ − 10 dB of 6.8 GHz can be obtained, which is much larger than that of its nonporous counterpart. Furthermore, the microwave absorption mechanism is discussed on the basis of the synergistic influence of micropores and TiO2 shell. This study provides a good reference for designing novel materials for electromagnetic interference applications.

Effect of three-step calcination on structural, magnetic and microwave properties of BaFe11.5Ti0.5O19 hexaferrite

BaFe12O19 and BaFe11.5Ti0.5O19 were prepared by three-step calcination method. Phase analysis and microstructural study were carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Site occupancy of Ti4+ ions with calcination step were investigated by Fourier-transform infrared (FTIR) and Raman spectroscopy. The magnetic and microwave properties (Ku-band) were measured by vibration sample magnetometer and vector network analyzer. XRD patterns confirmed the hexaferrite phase formation in all samples. FTIR showed the presence of Ti4+ ions at spin down octahedral and tetrahedral sites. The peak shift in FTIR and Raman spectra suggested that ion occupancy increases with calcination step. A drastic decrease in the coercivity was observed with substitution. Low dielectric and magnetic losses in were observed in Ti substituted samples. SEM revealed that Ti substitution promotes hexagonal grain with decreased size. Overall microwave absorbance was greatly improved by three step calcination method.

Structural and magnetic properties of V2O5-Na2SiO3 added Li0.5Fe2.5O4 spinel ferrite ceramics prepared by high energy ball milling

Spinel lithium ferrite ceramics inherently possess useful properties like high resistivity, saturation magnetization and Curie temperature, rectangular hysteresis loop and low dielectric and magnetic losses. They find widespread applications in high frequency electronic devices. Attempting an enhancement in the properties of interest, lithium ferrites were prepared by adding V2O5 and Na2SiO3 additives. Samples having Li0.5 Fe2.5O4 + (0.1) V2O5 + (x) Na2SiO3 as representative formula where x = 0.0, 0.05, 0.10, 0.15, 0.20, 0.25 were prepared by the ceramic technique using high energy ball milling. The prepared samples were calcined at 650 °C for 1h and sintered at 950 °C for 1h. XRD was done on the sintered samples and it is found that the samples possessed single phase with spinel structure. From the XRD data various structural parameters were evaluated. The microstructure of these samples was studied from the SEM micrograph. The room temperature frequency variation of initial permeability and permeability loss were measured in the range 5MHz to 40MHz using an impedance Analyzer. The results of these measurements are discussed in the paper.

Structural and impedance spectroscopy characterization of Soft Magnetic Materials

Abstract This work studies the relationship between the structural characteristics and the final magnetic properties of two different iron-based materials: one basic Soft Magnetic Material (SMM) and a Soft Magnetic Composite (SMC). The micrometric size of the starting powder, the pure iron composition of the core and the presence of a phosphate isolating shell in the composite sample were revealed by powder X-ray diffraction, Laser Diffraction and Fourier Transformed Infrared Spectroscopy respectively. Moreover, Scanning Electron Microscopy confirms the range of sizes of the powder samples and their non-perfect spherical shape. Magnetic and Impedance Spectroscopy measurements evidence the effects that the isolating shell has on the effective magnetic permeability and the relaxation frequency at which magnetic losses appear. Results obtained are of great interest from a technological point of view because the frequency range at which each material can effectively operate is measured. Furthermore, different structural aspects (such as particle size or the presence of an isolating shell) are related with the final functional properties. Besides, these results can help in the design of new soft magnets with lower magnetic losses over a wide range of frequencies.

Densification and magnetic properties of NiCuZn low-sintering temperature ferrites with Bi2O3-Nb2O5 composite additives

NiCuZn ferrite ceramics with high permeability and low magnetic loss have great values in high frequency applications. Here, we synthesized uniform and compact NiCuZn ferrites with small grains (about 1.5 μm) at 875 °C via adjusting additive amount of Nb2O5 and Bi2O3. The influence of Bi2O3 additives on the microstructure and magnetic properties of NiCuZn ferrite, especially for grain growth and grain size, have been investigated. SEM results indicated that Nb2O5 can obviously suppress grain growth when a small amount of Bi2O3 was added. Also, the liquid phase of Bi2O3 only can promote movement of grain boundary and reduce porosities between grains. Thus, a NiCuZn ferrite with high permeability (μi′ = 472.79), high saturation flux density (Bs = 0.313 T), high Q value (66.3) and low coercivity (Hc = 94.75 A/m) was obtained when 0.25 wt % Nb2O5-0.50 wt % Bi2O3 was added. It is proved that improvement of compactness can enhance magnetic properties even though grain growth was suppressed. However, over much Bi2O3 (more than 1.00 wt %) reduced the magnetic properties due to deterioration of grains uniformity and existence of non-magnetic Bi2O3 liquid phase. Such a low temperature solid phase synthesis method (i.e., adding composite additive with different melting point oxide) should also facilitate preparation of other advanced ceramics for practical applications.

Synthesis of chain-like ɑ-Fe/Fe3O4 core/shell composites exhibiting enhanced microwave absorption performance in high-frequency under an ultrathin matching thickness

Coaxial heterogeneous chain-like ɑ-Fe/Fe3O4 composites were synthesized by a facile two-step solvothermal method. The ɑ-Fe nanochains were first obtained by a simple liquid phase reduction process, and the ɑ-Fe/Fe3O4 core/shell composites were prepared by subsequent oxidation process. The electromagnetic properties of ɑ-Fe/Fe3O4 core/shell composites were measured with the coaxial reflection/transmission technique at 1.0–18.0 GHz. The ɑ-Fe/Fe3O4 core/shell composites have an optimal absorption peak value of about − 25.6 dB at 16.3 GHz and its effective absorption bandwidth lower than − 10 dB reaches 3.6 GHz (from 14.4 to 18.0 GHz). Importantly, the optimal absorption peak matching thickness of the absorber is only 0.8 mm. The enhanced microwave absorption performance is mainly originated from good impedance matching, which is related to low conductivity and magnetic loss of the coaxial heterogeneous chain-like ɑ-Fe/Fe3O4 core/shell composites. The reflection loss results indicate that the ɑ-Fe/Fe3O4 core/shell composites with thin thickness, wide absorption bandwidth and strong absorption characteristics can be used as excellent microwave absorption material in the high-frequency region.

Electromagnetic field effects in the microwave sintering of electrically conductive powders

Rapid sintering of compacted electrically conductive powders under heating by intense microwave radiation is investigated within a one-dimensional simulation model. The model accounts for the effective dielectric and magnetic properties of the powder material, electromagnetic field distribution, heat losses by thermal radiation, and densification. It is demonstrated that metal powders with insulating boundary layers on particles have low dielectric and magnetic losses, which results in a resonant character of microwave absorption. The influence of the interparticle contacts is investigated by introducing an effective electrical conductivity of the boundary layers, which can depend on the density. It is demonstrated that the losses in the boundary layers can stabilize the microwave heating process, facilitating rapid densification.

Structural, Magnetic and Microwave Properties of Gadolinium-Substituted Ca-Ba M-Type Hexagonal Ferrites

This paper presents a study on attempting to substitute Gd into a Ca-Ba M-type hexaferrite (Ca0.5Ba0.5GdxFe12−xO19, where x = 0, 0.05, 0.1, 0.15, 0.2, 0.25) using the sol–gel method. The structural, magnetic and microwave properties of the resultant material were investigated. Since Gd has a much larger ionic radius than Fe, substitution is not straightforward as revealed by the structural analysis. X-ray diffraction (XRD) patterns revealed some substitution into the M-type phase due to a changing lattice parameter; however, significant quantities of additional phases of hematite (α-Fe2O3) and gadolinium orthoferrite started to form at concentrations of up to Gd = 0.10 and at higher Gd concentrations, respectively. High-resolution transmission electron microscopy of selected compositions showed d-spacings corresponding to the three phases observed in XRD, confirming the incomplete substitution of Gd. Scanning electron microscopy showed platelet-shaped grains. Vibrating sample magnetometry at room temperature showed varied results owing to a myriad of interactions from the hexaferrite and secondary phases. The microwave complex permittivity and permeability in the frequency range of 2–11 GHz showed little frequency dependence with nominal values for the complex permeability. All the compositions exhibit low magnetic losses with frequency except Gd = 0.10. Such type of materials can be used for microwave devices in the low-GHz range and as well as permanent magnets.

The study of thermal, microstructural and magnetic properties of\xa0manganese\u2013zinc ferrite prepared by co-precipitation method using different precipitants

Mn–Zn ferrite was prepared from the solution after acid leaching of spent batteries by co-precipitation method using ammonia oxalate, sodium carbonate and sodium hydroxide as precipitating agents. The co-precipitation process was performed at temperature of over 50 °C by continuous magnetic stirring. The precipitates were pre-sintered at 850 °C in air. Dilatometric study has revealed that lowest shrinkage (only 5.6%) showed a material obtained from an oxalate precipitant. After pressing and high-temperature sintering at 1325 °C, it showed both insufficient density and the presence of pores, which contribute to the deterioration in the magnetic properties of the ferrites: the low magnetic permeability value and high magnetic losses. Ferrite prepared from hydroxide and carbonate precipitant showed a much higher shrinkage, sintered density and much higher magnetic permeability compared with the ferrite prepared from oxalate precursor.

High-Frequency Magnetic Properties of Ca-Substituted Co2Z and Co2W Barium Hexaferrite Composites

A series of Ca-substituted Z-type hexaferrites having nominal composition Ba3– x Ca x Co2Fe24O41 ( $x = 0$ –1.5) was studied for their high-frequency magnetic properties, including measurement of the permeability spectra and magnetic loss over a frequency range of 0.1–10 GHz. Analyses of crystal composition and microstructure reveal that hexaferrite composites consist of the Z-type phase and increasing amounts of the W-type phase were obtained as the Ca content was increased. Correspondingly, the permeability $\mu ^\prime $ displays a near linear decrease with x varying from 0 to 1.5, from ~8 to ~4.1 at 0.1 GHz. The relationship between permeability and variations in intrinsic magnetic parameters, i.e., saturation magnetization $M_{s}$ and coercivity $H_{c}$ , follows the Globus model. Compared with the undoped Z-type hexaferrite, the sample with $x = 0.2$ has lower magnetic loss over a broad frequency range, and higher levels of Ca substitutions ( ${x} \ge 1$ ) lead to low magnetic loss at high frequencies. The dual-phase composite of Co2Z and Co2W in proper ratio is an effective technique to improve the homogeneity of grain and microstructure, and thus reduce the high-frequency magnetic loss of the sintering hexaferrites.

Figure of merit of X‐type hexaferrite (Ba2Co2Fe28O46) for mobile antenna applications

AbstractWe report a Ba2Co2Fe28O46 (Co2X) hexaferrite, which has a high figure of merit (FOM = μ′/tan δμ) over the frequency range from 800 MHz to 1 GHz. The Co2X hexaferrite was prepared by the conventional solid‐state reaction. The calcined and sintered Co2X hexaferrites were characterized with a vibrating sample magnetometer and an impedance analyzer for their static and dynamic magnetic properties. The sintered Co2X hexaferrite shows 67.3 emu/g of saturation magnetization, 10.5 kOe of anisotropy field, and 0.03 of low magnetic loss tangent with relatively high permeability of 2.07 at 1 GHz, resulting in FOM of 69. This is the highest FOM among the reported microwave magnetic materials over the frequency range from 800 MHz to 1 GHz, which has not been previously reported. Therefore, the developed Co2X hexaferrite is suitable for antenna applications at the low‐frequency bands of mobile wireless communications.

Low loss, enhanced magneto-dielectric properties of Bi2O3 doped Mg-Cd ferrites for high frequency antennas

Mg1-xCdxCo0.05Fe1.95O4 ferrites are proposed for high frequency radar antennas, where x varies with the value of 0.0, 0.2, 0.3 and 0.4. With 5 wt% Bi2O3 added for low temperature co-fired ceramic (LTCC) application, the spinel ferrites synthesized at 930 °C reveal fairly excellent magnetic and dielectric properties. X-ray diffraction indicates the processed samples present normal spinel peaks and Bi24Fe2O39 (BFO) peaks. The existing BFO tailors the real part of magnetic permeability (ε′) and dielectric permittivity (μ′) to be approximately equal (x = 0.4, ε'≈μ'≈26) at a wide frequency range from 1 MHz to 100 MHz. Meanwhile, the LTCC-processed samples have ultra low dielectric loss tanδε and magnetic loss tanδμ (tanδε≈0.0008, tanδμ≈0.03, x = 0.3). In addition, the high saturation magnetization and appropriate coercivity mean enhanced magnetization. These eminent magneto-dielectric characteristics enable the materials to possess a farther study-worthy necessarity.

Design of a Patterned Soft Magnetic Structure to Reduce Magnetic Flux Leakage of Magnetic Induction Wireless Power Transfer Systems

A soft-magnetic-metal-based shield structure was designed to reduce magnetic flux leakage in magnetic-induction wireless power transfer systems. Soft magnetic metals have the advantages of high permeability and low magnetic loss, but have the disadvantage of high power loss owing to eddy current that is induced on the surface as a result of low-insulating characteristics. In order to solve this problem, a patterned soft magnetic metal was used to cut the route of the induced current. This decreases the power loss and reduces the leakage of magnetic field. A soft-magnetic-metal-based structure that has various patterns was designed to find the optimal structure for reducing the leaking magnetic field. By applying this structure to Wireless Power Consortium commercial A10 coil, the inductance, transfer efficiency, and magnetic flux leakage of the coil according to the material and the structure of the soft-magnetic-metal-based structure were observed. Fabrication and measurement tests were performed to verify the proposed structure, and it was found that the test results corresponded to the simulation results. It was confirmed that the proposed structure had a 84% thinner thickness compared with that of a conventional ferrite shield, an equivalent transfer efficiency of 74.5%, and a reduction in magnetic flux leakage of 20.9%.

Magnetic and Microwave Properties of Polycrystalline Gadolinium Iron Garnet

The microwave loss in nanosized GdIG particles synthesized using mechanical alloying technique was investigated. There were very few of research on the microwave properties of nanosized particle GdIG and there is no attempt investigating on the material at C-band frequency range and its correlation with the microstructure. Gadolinium (III) iron oxide and iron (III) oxide, α-Fe2O3 were used as the starting materials. The mixed powder was then milled in a high-energy ball mixer/mill SPEX8000D for 3 hours. The samples were sintered at temperature 1200°C for 10 hours in an ambient air environment. The phase formation of the sintered samples was analyzed using a Philips X’Pert Diffractometer with Cu-Kα radiation. Complex permeability constitutes of real permeability and magnetic loss factor were measured using an Agilent HP4291A Impedance Material Analyzer in the frequency range from 10 MHz to 1 GHz. A PNA-N5227 Vector Network Analyzer (VNA) was used to obtain the information on ferromagnetic linewidth broadening, ΔH that represents the microwave loss in the samples in in frequency range of 4 to 8 GHz (C-band). The ΔH value was calculated from the transmission (S21) data acquired from VNA. The single phase GdIG showed low initial permeability and low magnetic loss when applied with low-frequency range energy. From these data, it is validated that GdIG is a suitable material for microwave devices for the high-frequency range.

Bi2O3 enhances magnetic and dielectric properties of low temperature co-fired Ba(CoTi)1.20Fe9.6O19 ferrite composites in an oxygen atmosphere for applications in high frequency antennas

M-type barium ferrites Ba(CoTi)1.20Fe9.6O19 were synthesized with 5.0wt% Bi2O3 additive at low temperatures in an oxygen atmosphere. For temperatures increasing from 900°C to 945°C, the saturation magnetization (Ms) increased first and then decreased. However, coercivity (Hc) decreased first and then increased. Superfluous Bi2O3 produced BiFeO3 dielectric phase with Fe3+ ions. When the samples were processed in an oxygen atmosphere, the magnetic and dielectric properties were obviously increased, in particular, the real permeability (μ′) and real permittivity (ε′). The processed materials exhibited nearly equivalent real permeability and real permittivity (at 935°C, μ′≈ε′≈20.6), and had low magnetic loss (tanδμ≈0.05) and low dielectric loss (tanδε≈0.004) at the frequency of 100MHz. The results showed the Bi2O3 enhanced M-type barium ferrite was an excellent substrate material for high frequency antenna applications.

Preparation of high performance soft magnetic alloy Fe-4Si-0.8P by metal injection molding

Fe-4Si-0.8P soft magnetic alloy was prepared by metal injection molding (MIM). Ferrophosphorus liquid phase sintering promoted densification and enhanced magnetic properties. The sample with nearly full density, the saturation induction of 1.59T, maximum permeability of 2467, coercive force of 130A/m and resistivity of 81.2 μΩ·cm was obtained at 1300°C for 4h. Competitive properties contributed toward achieving low magnetic losses. Therefore, MIM Fe-4Si-0.8P can be widely used in the field of magnetic materials.

New Ferrimagnetic Garnets for LTCC-Technology Circulators

Abstract Yttrium iron garnet-based ferrites are used in nonreciprocal devices like microwave circulators and isolators. The low dielectric and magnetic losses of those materials provide the required properties. The main drawbacks of circulators are their size and cost, due to complex mechanical assembling of the different materials. To simplify the complex manufacturing process, a possible solution would be to adapt the different materials to a common low temperature cofired ceramic (LTCC) process: the circulators would be produced with an additive multilayer process. We showed that cationic substitutions (bismuth and copper) enable a considerable decrease of the sintering temperature of garnets, from ~1,450°C to down to ~950°C. Furthermore, due to bismuth cations, a high permittivity is achieved, allowing the reduction of the circulator core size. Our most recent results show that it is possible to decrease this temperature down to 880°C, thanks to vanadium substitutions. This significant decrease of the sintering temperature leads to a compatible material for cofiring with gold and particularly with silver (melting points 1,064°C and 962°C, respectively). Different assemblies of tapes were studied: ferrite with silver or gold, ferrite with dielectric and ferrite with dielectric and metallization. Physical analyses (dilatometry, coefficient of thermal expansion, etc.) are exposed and magnetic and dielectric properties (permittivity and saturation magnetization) are discussed. Moreover, the first results of circulators in LTCC technology with gold and silver screen printing are presented (transmission, isolation, and return loss) and the compatibility of the different elements is analyzed.