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Motivated by the wide application of the antiferromagnetic/ferromagnetic (FM) bilayer structures in high-frequency microwave magnetic devices, the Si/NiO/Ni81Fe19 films with different orientations of NiO buffer layer are deposited by magnetron sputtering technology. The phase, microstructure, hysteresis loop, and angular dependence of FM resonance (FMR) linewidth are investigated by X-ray diffractometer, field-emission scanning electron microscope, atomic force microscope, vibrating sample magnetometer, and electron spin resonance spectrometer, respectively. The Si/NiO(220) film has much smaller grain size than that of Si/NiO(200) film, which is beneficial to grow a high quality NiFe film on Si/NiO(220)/NiFe bilayer structures. The hysteresis loop of Si/NiO(220)/NiFe films shows an obvious exchange bias and a relatively smaller coercivity. The FMR linewidth ( $\Delta {H}$ ) of Si/NiO(220)/NiFe films is much smaller than that of Si/NiO(200)/NiFe films, which is caused by the different structural properties and morphologies of the NiO buffer layer. The Lande $g$ factors and effective damping parameters $\alpha_{\rm eff}$ are also discussed.

Ni-substituted manganese–zinc (MnZn) ferrites with the composition of Mn0.506– x Zn0.244Ni x Fe2.250O4.0 ( $x = 0.066{\sim}0.122$ ) have been prepared by the solid-state reaction method. The cation distribution has been investigated by the Rietveld refinement of X-ray diffraction patterns, the microstructure has been observed using a scanning electron microscope, and the magnetic property has been measured using superconductor quantum interference devices and $B$ – $H$ analyzer. The results show that Zn2+ and Ni2+ ions prefer to occupy the tetrahedron site (A sublattice) and octahedron site (B sublattice), respectively. However, Mn2+ and Fe3+ ions can enter into A and B sublattices, where the ratio of Mn2+ ions occupying A and B sublattices is 4:1. The lattice parameter ( $a$ ) of the samples decreases with the increase of Ni-substituted content. Meanwhile, based on the Neel model of collinear-spin ferrimagnetism, the molecular-field coefficients $\omega _{\rm AA}$ , $\omega _{\rm BB}$ , and $\omega _{\rm AB}$ of the Ni-substituted MnZn ferrites have been calculated, and the magnetic moment of A and B sublattices versus temperature $T$ has also been investigated. The fitting results match well with the experimental data. Both $\omega _{\rm AB}$ and $\omega _{\rm BB}$ increase with the increase of the Ni-substituted content, but $\omega _{\rm AA}$ shows the opposite variation trend. The Curie temperature also increases with the increasing of the Ni-substituted content, which is attributed to the enhancement of superexchange interaction for A–B sublattice. In addition, the temperature dependence of initial permeability and core loss has been discussed.

Barium hexaferrites BaFe12O19 with Bi2O3/CuO additives were synthesized by the conventional oxide ceramic process. The results manifest that Bi2O3 additives mainly concentrate on the grain boundary regions, while CuO additives could both enter into the grain and segregate at the grain boundary regions. The appropriate sintering temperature of barium hexaferrites with Bi2O3 and Bi2O3 + CuO additives reaches 1020 °C and 920 °C, respectively. As the amount of Bi2O3 is 3 wt%, the specimens of BaFe12O19 show saturation magnetization ( Ms ) of 346 kA/m, remanence ( Mr ) of 227 kA/m, and density ( d ) of 5.06 g/cm3. Meanwhile, the combination of 3 wt% Bi2O3 and 3 wt% CuO additives significantly promotes grain growth and sintering densification, with a high saturation magnetization of 371 kA/m and density of 5.23 g/cm3 for BaFe12O19, which are pretty close to the theoretical values (380 kA/m, 5.28 g/cm3). Moreover, the corresponding remanence could also rise by 10% compared with that in the sintered samples with 3 wt% Bi2O3.

NiZn ferrites have been extensively applied in various electromagnetic devices such as inductors and anti-EMI circuits due to some frequency-dependent physical properties like magnetic permeability. As a key parameter in radiofrequency devices, frequency properties of the permeability are determined by the magnetization mechanisms. Generally, there are two magnetization mechanisms contributing to the permeability dispersion spectra: domain wall motion and spin rotation. To investigate the respective contribution from each mechanism, various efforts have been made recently. By resolving the permeability dispersion spectra, T. Tsutaoka [1] have studied that domain wall contribution to permeability decreased with the decrease of the amount of domain wall when NiZn particles were coated with polyphenylene sulfide. Similar simulation procedures were also adopted by M. Han [2] in NiZn ferrites doped with SiO 2 , and the results indicated that the components of spin rotation make larger contributions to the permeability dispersion spectra because the SiO 2 aggregated at the NiZn ferrite grain boundaries. J. Hu [3] have taken CuO and V 2 O 5 additives as variables to reduce the sintering temperatures of NiZn ferrites, and it was deduced from the fitting results that domain wall motion plays a predominant role in the magnetizing process and the loss mechanism at low frequency like 100 kHz. H. Su [4] et al. have varied the sintering temperature of the NiZn ferrite with fixed composition in order to obtain different microstructures, and it was found that larger grain size is favorable for domain wall motion. However, detailed influence of anisotropy and magnetic domain are rarely mentioned on the superposition of the two different magnetization mechanisms. In this paper, combined with a comprehensive analysis of relevant magnetic properties and magnetic domain, the change of contribution from two kinds of magnetization mechanisms was discussed.