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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. [ABSTRACT FROM AUTHOR]

Two series of W- and M-type composite hexaferrites were synthetized using the conventional ceramic method in two different synthesis routes. In the first synthesis route, W- and M-type composite hexaferrites were formed by reaction in the pre-sintering stage. In the second synthesis route, W- and M-type composite hexaferrites were obtained by physically mixing W- and M-type hexaferrites in the second ball milling stage. The influence of M-type phase on the structure and magnetic properties of W-type hexaferrites synthesized in both synthesis routes are investigated in detail. For both synthesis routes, X-ray diffraction (XRD) patterns of all samples indicated crystallization of W- and M-type hexaferrites phase and scanning electron microscopy (SEM) measurements revealed hexagonal platelet-like grains. In the pre-sintering stage, the saturation magnetization (4π M s) of all samples ranged between 3.30 kG and 4.25 kG. The remanence ratio (M r / M s) changed from 0.77 to 0.88 with the increase of pre-sintering temperature. The coercivity (H c) of all samples ranged between 456 Oe and 1846 Oe. The ferromagnetic resonance (FMR) linewidth (Δ H) ranged between 466 Oe and 748 Oe. In the second ball milling stage, 4π M s and M r / M s maintained a relatively stable value of ~4.5 kG and ~0.89, respectively. H c increased from 519 Oe to 620 Oe with the increase of M-type hexaferrites. Δ H ranged between 317 Oe and 573 Oe. We note that in both synthesis routes only the composite hexaferrites synthesized in the pre-sintering stage have a significantly improved coercivity from 456 Oe to 1846 Oe. This enhancement in coercivity is attributed mainly to the effect of exchange coupling among ferrite grains. In addition, the Δ H decreases with the addition of M-type hexaferrites. [ABSTRACT FROM AUTHOR]

Strontium ferrites, which exhibit large remanence, high coercivity (H c), are fascinating for applications in motors and high-frequency microwave devices. Here we demonstrate the strontium ferrites (Sr 0.34 Ca 0.25 La 0.41 Fe 11.4 Co 0.19 O 19-δ) sintered at 1150 °C with enhanced magnetic properties through constructing magnetoelastic stress. The effects of applied pressure (P c -axis) of 0–16 kPa during the sintering process on phase compositions, morphologies, magnetic and microwave properties are investigated in detail. We note that the P c -axis could contribute to enhanced c -axis preferred orientation. This mechanism of enhancement has been also discussed according to the magnetoelastic theory. By applying an external pressure of 8 kPa, intrinsic coercivity (H cj) of 4657 Oe and magnetic coercivity (H cb) of 3781 Oe are obtained. The increments are 8.1% and 18.0% for H cj and H cb , respectively, compared to the sample with P c -axis of 0 kPa. However, the enhancement of H c by the P c -axis is seen to be limited above 8 kPa, which can be attributed to the enlarged grain size and porosity observed. In addition, the ferromagnetic resonance frequency (f r) is also increased by the increased P c -axis. [ABSTRACT FROM AUTHOR]

M-type hexaferrites which exhibit strong uniaxial anisotropy field, are promising for the applications in self-biased microwave and millimeter wave (MMW) devices. Here we demonstrate crystallographically textured hexaferrites with narrow ferromagnetic resonance (FMR) linewidth synthesized by the conventional ceramic method. Meanwhile, the relationship between iron-deficiency content and microstructure, crystallographic, and magnetic properties are researched. These hexaferrites have strong remanence ratio of above 0.9 along c -axis. By fitting of Lorentzian function to absorption derivative, we probe detailedly into the zero-field FMR linewidth of Ba 0.8 La 0.2 Fe 11.8- x Cu 0.2 O 19-δ hexaferrites. When x equals 1.0, it indicates the narrowest FMR linewidth of 324Oe, as compared with previous reports for crystallographically textured hexaferrites. [ABSTRACT FROM AUTHOR]

M-type Sr (SrM) hexaferrites have been widely applied in millimetre/microwave ferrite devices such as circulators and isolators. SrM hexaferrites must exhibit a high remanence ratio M r / M s , a high anisotropy field H a , and a low ferromagnetic resonance (FMR) linewidth Δ H to further develop millimetre/microwave equipment and devices with high frequencies, miniaturisation, and planarisation. However, it is difficult for M-type hexaferrite to simultaneously meet the requirements of high M r / M s , high H a , and low Δ H , which are key to realising high-frequency self-biased ferrite devices. In this work, Ca–La–Co-substituted SrM ferrite was prepared, and the influence of La substitution on the micromorphology, static magnetic properties, and Δ H values of SrM hexaferrites is discussed in detail. The results demonstrated that as the La substitution content x increased from 0.0 to 0.5, the saturation magnetisation 4π M s and coercivity H c initially increased, and then decreased. The H a values of all samples were higher than 18 kOe. The FMR linewidth Δ H initially increases, and then decreased after reaching a maximum value at x = 0.2. The independent grain approximation theory was used to analyse the changing trend of the FMR linewidth. The results showed that the crystalline anisotropy linewidth Δ H a accounted for a larger proportion of the FMR linewidth than the porosity linewidth Δ H p. The sample with a La substitution content x of 0.3, exhibited the best performance (4π M s = 3915 Gs, 4π M r = 3387 Gs, H c = 1818 Oe, M r / M s = 0.865, large H a = 23.99 kOe, and Δ H = 1548 Oe at 58.8 GHz). The materials prepared in this research have significant potential for application in high-frequency self-biased devices and microwave engineering. [ABSTRACT FROM AUTHOR]

NiCuZn (NCZ) ferrites have been widely used in non-reciprocal microwave/millimeter ferrite devices, such as circulators. With the development of microwave/millimeter devices and components to high frequency, miniaturization, and lightweight applications, NCZ ferrites have needed to satisfy the essential requirements of high saturation magnetization 4π M s , low coercivity H c , and low ferromagnetic resonance (FMR) linewidth Δ H. Herein, 0.1 wt% Bi 2 O 3 and 0.0–3.5 wt% CaCu 3 Ti 4 O 12 (CCTO) composite additives were introduced to NCZ ferrites, the influence of Bi 2 O 3 –CCTO composite additives on micromorphology, static magnetic properties, and FMR linewidth Δ H of NCZ ferrites have been demonstrated in detail. The results show that increasing the CCTO amounts in NCZ ferrites, saturation magnetization 4π M s monotonically decreases from 5484Gs to 4819Gs, and both coercive force H c and FMR linewidth Δ H first decreases and then increases with minimums of 31A/m and 147Oe, respectively. In addition, the theory of spin-wave narrowing and the law of approach to saturation have been adopted for the separation calculation of FMR linewidth Δ H to the crystalline anisotropy linewidth Δ H a and porosity induced linewidth Δ H p. The sample with 0.1 wt% Bi 2 O 3 and 1.5 wt% CCTO possesses high saturation magnetization 4π M s (5321Gs), remanence B r (200 mT), low coercivity H c (31A/m), and low FMR linewidth Δ H (147Oe). The state-of-the-art NCZ ferrites with outstanding performances manifest significant applied potency for microwave/millimeter devices and components in phase array radar systems. [ABSTRACT FROM AUTHOR]

• Magnetic properties of SrM hexaferrites are regulated by changing Bi 2 O 3 additive. • All samples showed strong uniaxial anisotropy as Bi 2 O 3 additive amount increased. • When Bi 2 O 3 additive x = 1.0 wt%, the overall performance of sample is the best. • Theory of independent grain approximation was adopted to divide the FMR linewidth. Considering the improvement of electronics regarding high frequency and miniaturization, SrM hexaferrites need to exhibit high anisotropy field H a , high remanence ratio M r / M s , and low ferromagnetic resonance linewidth Δ H to create microwave devices and equipment with planarisation, miniaturisation, and high frequencies. The key to achieving self-biased microwave devices with high-frequency is to simultaneously achieve high H a , high M r / M s , and low Δ H. However, it is hard to meet these requirements. In this study, Sr 0.4 La 0.3 Ca 0.3 Fe 11.85 Al 1.0 Co 0.15 O 19 was used to study the effect of different doping amounts of Bi 2 O 3 on its magnetic characteristics, micromorphology and FMR linewidth. With the increase of Bi 2 O 3 doping, the grain size of the sample gradually increased, and the uniformity of the grain size gradually decreased. When the Bi 2 O 3 doping amount x increased from 0 to 1.2 wt%, the 4π M s and 4π M r values increased and the coercivity displayed the opposite tendency. The samples showed great uniaxial anisotropy. The magnetocrystalline anisotropy field H a shows a trend of initially decreased and then increased. When x = 1.0 wt%, H a reaches the maximum value of 28.9 kOe. At this time, the ferromagnetic resonance linewidth Δ H of the sample is 1578 Oe. The theory of IGA was adopted to divide the FMR linewidth into two parts Δ H a and Δ H p. Accroding to the results, Δ H a takes the bigger proportion of linewidth. However, the change in Δ H p is not negligible. When x = 1.0 wt%, the sample showed its best performance (4π M s = 3412 Gs, 4π M r = 2905 Gs, H c = 2649 Oe, M r / M s = 85.1%, large H a = 28.864 kOe, and Δ H = 1578 Oe). The SrM ferrite materials provided in this study can potentially be used in the microwave engineering, high-frequency, and self-biased devices. [ABSTRACT FROM AUTHOR]