Acher's constraint on the high-frequency magnetic performance of composites (original) (raw)
Related papers
High-frequency behavior of magnetic composites
Journal of Magnetism and Magnetic Materials, 2009
The paper reviews recent progress in the field of microwave magnetic properties of composites. The problem under discussion is developing composites with high microwave permeability that are needed in many applications. The theory of magnetic composites is briefly sketched with the attention paid to the laws governing the magnetic frequency dispersion in magnetic materials and basic mixing rules for composites. Recent experimental reports on the microwave performance of magnetic composites, as well as data on the agreement of the mixing rules with the measured permeability of composites that are available from the literature are discussed. From the data, a conclusion is made that the validity of a mixing rule is determined by the permeability contrast in the composite, i.e., the difference between permeability of inclusions and that of the host matrix. When the contrast is low, the Maxwell Garnet mixing rule is frequently valid. When the contrast is high, which is of the most interest for obtaining high microwave permeability of a composite, no conventionally accepted theory is capable of accurately predicting the permeability of the composites. Therefore, the mixing rules do not allow the microwave properties of magnetic composites to be predicted when the permeability of inclusions is high, that is the case of the most interest. Because of that, general limitations to the microwave performance of composites are of importance. In particular, an important relation constraining the microwave permeability of composites follows from Kittel's theory of ferromagnetic resonance and analytical properties of frequency dependence of permeability. Another constraint concerning the bandwidth of electromagnetic wave absorbers follows from the Kramers-Kronig relations for the reflection coefficient. The constraints are of importance in design and analysis of electromagnetic wave absorbers and other devices that employ the microwave magnetic properties of composites, such as magnetic substrates for microwave antennas, microwave inductors, etc.
High frequency permeability of ferromagnetic metal composite materials
Journal of Magnetism and Magnetic Materials, 2007
Complex permeability ðm à ¼ m 0 À im 00 Þ spectra of ferromagnetic metal (cobalt and permalloy) granular composite materials have been studied in the microwave frequency range. High surface electrical resistance in ferromagnetic metal particles can be obtained by the heattreatment; the eddy current effect in high frequency permeability is suppressed in the high particle content composite materials. The 70 vol.% permalloy and 79 vol.% cobalt composite materials containing the heat-treated particles have a negative and zero permeability at several GHz, respectively.
Journal of Magnetism and Magnetic Materials, 2019
A new method of studying microwave magnetic properties of metal particles and films is developed. The method is based on measurements with swept frequency under magnetic bias in a coaxial line. Application of the technique is illustrated by the data obtained for two types of samples, washershaped rolls of thin ferromagnetic films and composites filled with flake Sendust particles. The treatment of the measured data is performed with an account for sample demagnetization and anisotropy. The values of the anisotropy field and the saturation magnetization of thin iron films are calculated considering demagnetization of the sample. Because of the anisotropy of the composite samples, permeability depends slightly on the length of samples, and the saturation magnetization and the anisotropy field cannot be determined.
A mixing rule for predicting frequency dependence of material parameters in magnetic composites
Journal of Magnetism and Magnetic Materials, 2012
A number of mixing rules are proposed in the literature to predict the dependence of effective material parameters (permittivity and permeability) of composites on frequency and concentration. However, the existing mixing rules for frequency dependence of permeability in magnetic composites typically do not provide satisfactory agreement with measured data. Herein, a simple mixing rule is proposed. Its derivation is based on the Bergman-Milton spectral theory. Both the Bruggeman effective medium theory and the Maxwell Garnett approximation are included as particular cases of the proposed mixing rule. The derived mixing rule is shown to predict accurately the frequency dependence of permeability in magnetic composites, which contain nearly spherical inclusions.
Ferromagnetic Resonance and Antiresonance in Composite Medium with Flakes of Finemet-Like Alloy
Nanomaterials, 2021
Propagation of microwaves is studied in a composite material containing flakes of Fe-Si-Nb-Cu-B alloy placed into an epoxyamine matrix. The theory is worked out, which permits to calculate the coefficients of the dynamic magnetic permeability tensor and the effective magnetic permeability of the transversely magnetized composite. The measurements of magnetic field dependences of the transmission and reflection coefficients were carried out at frequencies from 12 to 38 GHz. Comparison between calculated and measured coefficients were conducted, which show that the calculation reproduces all main features of the resonance variations caused by ferromagnetic resonance and antiresonance. The dissipation of microwave power was calculated and measured. It is shown that the penetration depth of the electromagnetic field increases under antiresonance condition and decreases under resonance.
Modeling the Magnetoelectric Composites in a Wide Frequency Range
Materials
This article presents a general theory of the ME effect in composites in the low- and high-frequency ranges. Besides the quasi-static region, the area of electromechanical resonance, including longitudinal, bending, longitudinal shear, and torsional modes, is considered in more detail. To demonstrate the theory, expressions of ME voltage coefficients are obtained for symmetric and asymmetric layered structures. A comparison is made with the experimental results for the GaAs/Metglas and LiNbO3/Metglas structures. The main microwave ME effect, consisting of the FMR line shift in an electric field, for the ferromagnetic metals, their alloys, and YIG ferrite using various piezoelectrics is discussed. In addition to analytical calculations, in the article, finite element modeling is considered. The calculation methods and experimental results are compared for some composites.
Microwave permeability of Co[sub 2]Z composites
Journal of Applied Physics, 2005
The microwave permittivity and permeability of Co 2 Z barium ferrite composite samples are measured as functions of frequency and volume fraction of the ferrite. Magnetostatic properties of the bulk ferrite are determined. This allows Snoek's law [J. L. Snoek, Physica 14, 204 (1948)] to be verified by comparing the microwave and magnetostatic Snoek's constants. The modification of Snoek's law for hexagonal ferrites suggested recently by Acher et al. [Phys. Rev. B 62, 11324 (2000)] is also verified. Acher's constant is found from microwave measurements to agree with the value calculated from the magnetostatic properties of bulk ferrite, but microwave and magnetostatic Snoek's constant do not agree. This may be attributed to the effect due to demagnetizing factors of ferrite inclusions that are not considered in the derivation of Snoek's and Acher's laws. The measured frequency-dependent permeability of composites satisfies the Lorentzian dispersion law and is consistent with the Maxwell Garnett approximation [J. C. Maxwell Garnett, Philos. Trans. R. Soc. London 203, 385 (1904)]. According to the theoretical analysis based on the Lorentzian dispersion law and the Maxwell Garnet mixing rule, both Snoek's and Acher's constants must be linear functions of the volume fraction, independent of whether microwave values of the constants are in agreement with the magnetostatic values. In contrast, the experimental measurements reveal a steady decrease of both constants with the volume fraction. The disagreement is discussed in terms of the influence of effective medium in composite on the inherent permeability of ferrite particles.
Predicting of wideband electromagnetic responses of composites containing magnetic inclusions
2010 IEEE International Symposium on Electromagnetic Compatibility, 2010
Engineering of absorbing bulk and sheet composite materials, including nanocomposites, for various EMI applications, requires adequate prediction of frequency and concentration behavior of these composites. This paper proposes two simple analytical formulations for effective permittivity and permeability of magneto-dielectric composites as functions of frequency and concentration. The first new proposed mixing rule is based on the GhoshíFuchs theory, which gives good agreement with the measured permittivity and permeability for composites containing magnetic alloy powders. This approach employs the Bergman-Milton concept of spectral function. Herein, the spectral function typical for the Bruggeman effective medium theory, also known as the Bruggeman symmetric rule (BSR), is chosen. This spectral function is composed using two fitting parameters: an averaged shape factor of inclusions, and the percolation threshold. These fitting parameters are found from the concentration dependence of permittivity, and then they are used to retrieve frequency dependence of permeability. The proposed mixing law is valid for nearly spherical inclusions in the composite, e.g., crumbs. Another analytical model proposed in this work can be applied to predict effective permeability of composites containing magnetic inclusions. It is based on the Bruggeman asymmetric rule (BAR), which has been modified in such a way that it takes into account shape factors of magnetic inclusions, in particular, randomly oriented platelets.
Wide Frequency Range AC Magnetic Properties of Fe-Based Composite Materials
Acta Physica Polonica A, 2010
The aim of this work was to analyze the influence of resin content on contribution of the hysteresis, eddy current and anomalous losses to the total losses in the frequency range from DC to 150 kHz. The samples of composite material were prepared in the form of the ring with outer diameter of 25 mm, inner diameter of 17 mm and height approximately 3 mm and in the form of cylinder with diameter of 25 mm and height approximately 3 mm by a compaction of mixture of iron powder ASC100.29 (90 vol.%) and commercial termoset resins. The DC hysteresis losses were obtained by the measurements of DC hysteresis loops and the total power losses in the frequency range 0.4 Hz-150 kHz from AC hysteresis loops, both at maximum induction 0.05, 0.1 and 0.2 T. The magnetic properties of the composite rings were compared with the properties of the material prepared from the powder supported by Höganäs AB Sweden. By analyzing the frequency dependence of total losses of the Fe-based SMC we found out that hysteresis losses contribute to the total losses as a majority component.