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The microwave properties of epoxy composites filled with 30 wt.% of BaFe12–xGaxO19 (0.1 ≤ x ≤ 1.2) and with 1 wt.% of multi-walled carbon nanotubes (CNTs) were investigated in the frequency range 36–55 GHz. A sufficient increase in the microwave shielding efficiency was found for ternary 1 wt.%CNT/30 wt.% BaFe12–xGaxO19/epoxy composites compared with binary 1% CNT/epoxy and 30 wt.% BaFe12–xGaxO19/epoxy due to the complementary contributions of dielectric and magnetic losses. Thus, the addition of only 1 wt.% of CNTs along with 30 wt.% of barium hexaferrite into epoxy resin increased the frequency range where electromagnetic radiation is intensely attenuated. A correlation between the cation Ga3+ concentration in the BaFe12–xGaxO19 filler and amplitude–frequency characteristics of the natural ferromagnetic resonance (NFMR) in 1 wt.%CNT/30 wt.% BaFe12–xGaxO19/epoxy composites was determined. Higher values of the resonance frequency fres (51.8–52.4 GHz) and weaker dependence of fres on the Ga3+ concentration were observed compared with pressed polycrystalline BaFe12–xGaxO19 (fres = 49.6–50.4 GHz). An increase in the NFMR amplitude on the applied magnetic field for both random and aligned 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composites was found. The frequency of NFMR was approximately constant in the range of the applied magnetic field, H = 0–5 kOe, for the random 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composite, and it slightly increased for the aligned 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composite.

Yttrium iron garnet (Y3Fe5O12, YIG) ferrite has excellent magnetic properties that are suitable for microwave communication devices. In the present research, Ca-Zr co-substituted Y1.83−xBi1.17CaxFe5−xZrxO12 (YBiIG, x = 0.00–0.15 with a step of 0.05) ferrites were prepared by a solid-state reaction method to enhance microwave magnetic and dielectric properties. The phase formation, microstructure, and magnetic and dielectric properties of the materials were investigated by x-ray diffraction, scanning electron microscopy, impedance analyzer, vibrating sample magnetometer (VSM), and ferromagnetic resonance (FMR) linewidth. The results showed that Ca2+-Zr4+ ions did not change the phase formation of the ferrites and enhanced the magnetic permeability μ′ (μ′ = 24.10 at 10 MHz, x = 0.15) and dielectric constant (ε′ = 24.55 at 10 MHz, x = 0.15). Meanwhile, the specific saturation magnetization (σs) increased from 20.26 emu/g to 22.79 emu/g with the increase of Ca-Zr substitution, and the FMR linewidth (ΔH) decreased from 406.34 Oe to 339.60 Oe. The work showed that the high dielectric constant exhibited by Ca-Zr-substituted YBiIG ferrite materials has potential application value in high-frequency microwave device applications, such as circulators, isolators, phase shifters, and other microwave components.

This work presents a new methodology for fabrication of membrane-assisted elongated YIG nanostructures through the sol-gel method using low-cost materials, and the estimation of the average size of the geometries formed within the pores through ferromagnetic resonance measurements. A precursor solution was deposited on the internal surface of porous aluminum oxide membrane, using an assembly consisting of a vacuum system coupled to an apparatus, which assists in the entry of the used precursor solution, breaking the barriers related to the existing surface tension, with subsequent heat treatment to form the single phase of yttrium iron garnet (YIG). The data collected by X-ray diffraction and Raman spectroscopy indicated this result. The study of the contact angle of the precursor solution and the alumina template indicated great compatibility, an angle of 35.4°. SEM analysis showed that elongated structures were deposited inside the pore’s walls, with different lengths up to 3 micrometers and the EDS analysis showed the presence of the main elements of the YIG phase. The Kittel’s equation and FMR spectral data were used to estimate the mean size of the elongated nanostructures. We found six different size categories with 1856, 1768, 1661, 1588, 1570, 1498 nm . The methodology proved to be efficient for the characterization of elongated YIG nanostructures, becoming a perspective of future applications. Graphical Abstract Highlights Setup for the infiltration of the alumina membrane with the YIG precursor was proposed. Elongated YIG structures were obtained with diverse potential applications. The FMR was used to estimate the mean size of elongated YIG structures.

The magnetic and microwave properties of nanocomposites containing iron particles encapsulated in a carbon shell (Fe@C), as well as carbon nanotubes (CNT), have been experimentally studied. The examination of magnetic properties of composites shows that the materials under study contain a ferromagnetic component. The availability of ferromagnetic ordering for the dielectric matrix-based nanocomposite sample with Fe@C particles has been confirmed by the measurement results of the transmission and the reflection coefficients of the microwaves, since the ferromagnetic resonance has been observed. Furthermore, in the fields less than the field of ferromagnetic resonance, there are the signs of the presence of ferromagnetic antiresonance. The ferromagnetic resonance leads to minima in the transmission and reflection coefficients, whereas the antiresonance, conversely, leads to maxima in the reflection coefficient. The measurement results have been compared with the theoretical calculations of the field dependence of microwave transmission and reflection coefficients.

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.

The structure, magnetic properties and ferromagnetic resonance curves of cobalt ferrite particles synthesized by chemical coprecipitation technique have been studied. The possibility of resonant heating of powder in a magnetic anisotropy field of particles is shown, which can find application in medicine for magnetic hyperthermia.

The absorption of waves of the centimeter and millimeter wavebands in composites with Finemet alloy particles and carbon nanotubes has been studied. It has been established that ferromagnetic resonance and antiresonance are observed in such composites. A method is proposed for calculating the effective dynamic magnetic permeability of a composite containing both a random distribution of ferromagnetic particles and a part of the particles oriented in the same way. In the approximation of effective parameters, the dependences of the transmission and reflection coefficients of microwaves are calculated. It is shown that the theoretical calculation confirms the existence of resonant features of these dependences caused by ferromagnetic resonance and antiresonance. The theory based on the introduction of effective parameters satisfactorily describes the course of the field dependence of the coefficients and the presence of resonance features in these dependences. The frequency dependence of the complex permittivity of the composite is determined. The dependence of the complex magnetic permeability on the magnetic field for millimeter-wave frequencies is calculated.

Understanding the origin and mechanisms of magnetic damping in complex oxide materials is crucial for optimizing spin dynamics and tailoring their properties for specific spintronic applications. Ferromagnetic resonance spectroscopy (FMR) technique has been used to investigate the magnetic damping of multiple La2/3Sr1/3MnO3 (LSMO) epitaxial thin films with similar thickness and identical DC magnetic properties. However, the dynamic magnetic properties exhibit noticeable variations among samples. Microstructural analyses using X‐ray diffraction (XRD) and atomic force microscopy (AFM), confirm that the samples are structurally identical, except for minute differences in the miscut angles of the substrates. Nevertheless, when examining the samples using backscattered electron (BSE) images in scanning electron microscopy (SEM), significant disparities in the twin distribution are observed. These variations in the twin distribution directly correlate with the observed differences in the damping values. A careful image analysis of BSE images allows to demonstrate that the increase of damping is due to the pinning of the magnetization in the twin boundaries. Ferromagnetic resonance spectroscopy is used to study magnetic damping in epitaxial La2/3Sr1/3MnO3 thin films. Backscattering scanning electron microscopy images show significant disparities in the twin's distribution in otherwise identical samples, which correlate with changes in damping values. A meticulous analysis of these images shows that the increased damping is the result of magnetization pinning at twin's boundaries.

Spin-transfer ferromagnetic resonance in a planar external magnetic field is used to perform an experimental study of the effect produced by broadband rectification of a microwave current in magnetic tunnel junctions with perpendicular magnetic anisotropy. It is found that the parameters of broadband rectification (frequency range, rectified voltage, and the region of the mode of ferromagnetic resonance) depend on the size and its shape of the sample. The maximum rectified voltage is observed on a round elliptical sample of 100 × 150 nm. At the same time, the widest operating frequency range of approximately 2 GHz was observed on strongly elliptical MTJs with sizes of 75 × 250 nm 2 .

Inductance of an on-chip transmission line with a magnetic film-type noise suppressor is quantitatively evaluated based on magnetic circuit analysis to develop design guidelines. A Co85Zr3Nb12(Co-Zr-Nb) film with uniaxial anisotropy deposited on a coplanar waveguide (CPW) was used as a test bench, and a magnetic circuit model was developed with cross-sectional size and material parameters. The magnetic circuit analysis included the ferromagnetic resonance (FMR) frequency shift caused by an additional demagnetizing field due to the presence of the narrow CPW. The inductance calculated using the reluctance around the signal line was almost the same as measured values. Results of this study indicated that the frequency characteristics of the inductance were mostly affected by the real part of the complex permeability considering the demagnetizing field.