Microwave Permeability Spectra Research Articles

Absorption Characterization of Mn-Zr-Substituted La-Sr Hexaferrite Using Open-Circuit and Short-Circuit Approaches in 8.2–18 GHz Frequency Range

The present study reports on the microwave absorption characterization of Mn2+-Zr4+ substituted lanthanum strontium ferrites, Sr0.85La0.15(MnZr) x Fe12−2x O19, where x = 0.0, 0.25, 0.50, 0.75 and 1.0 in the X- and Ku-band. The synthesized ferrites are characterized with regard to their electromagnetic properties such as complex permittivity \( \left( {\varepsilon^{\prime} - j\varepsilon^{\prime\prime}} \right) \) and complex permeability \( \left( {\mu^{\prime} - j\mu^{\prime\prime}} \right) \) using vector network analysis in the 8.2–18 GHz frequency range. Real and imaginary parts of permittivity decrease with the increase in Mn-Zr concentration due to a reduction in electron hopping conduction and eddy current losses, respectively. Microwave permeability spectra are also affected by the doping. The amplitude of magnetic loss peak increases with the increase in doping except for the x = 1.0 composition. Two commonly used approaches, open-circuit and short-circuit, have been employed for the absorption analysis. The difference in the results of these two techniques is justified on the basis of the reflection mechanism. The presented experimental findings underline the potential of the synthesized compositions with Mn-Zr concentrations x = 0.25, 0.5 and 0.75 in the suppression of electromagnetic reflections and radar signatures.

Enhancement of in-plane uniaxial magnetic anisotropy for patterned nanoparticle films fabricated by electric field-assisted deposition

The patterned FeNi nanoparticle films with strip width 60µm were prepared by electric field-assisted deposition technique. Application of electric field drove the accelerating deposition of the condensed nanoparticles, promoting the formation of the films with high stacking density. Besides the excellent soft magnetic characteristics, the samples showed an obvious enhancement of in-plane uniaxial magnetic anisotropy when they were annealed in vacuum environment at proper temperatures. The increase of in-plane uniaxial magnetic anisotropy, which is due to the release of stress with increasing temperature, is also confirmed by scanning microwave permeability spectra in GHz range. The experimental results imply that optimization of in-plane uniaxial magnetic anisotropy is particularly attractive for the application of electric field deposited soft magnetic nanoparticle films in the high-temperature processing electromagnetic devices.

Improvement of microwave permeability spectra in high stacking density FeNi nanoparticle films prepared by electric field-assisted deposition

We proposed an advanced method to improve saturation magnetization of soft magnetic nanoparticle films, which are of great concern for application in modern electromagnetic devices operated in the GHz range. Fe50Ni50 nanoparticle films with a particle size of about 6 nm were fabricated at room temperature by electric field-assisted deposition. An electric field of 10–20 kV was applied on the deposition platform during the film’s manufacture to obtain high stacking density and superior in-plane soft magnetic properties in the films. Based on the results of the microwave permeability spectra, it is found that the samples with higher saturation magnetization have excellent microwave response. These results indicate that magnetic softness and microwave behavior of FeNi nanoparticle films can be modulated by applying electric field during deposition.

Fabrication of Co90Zr10 thin films with adjustable resonance frequency from 1.8 to 7.1 GHz

A series of Co90Zr10 thin films deposited at different oblique angles from 10° to 70° was prepared by radio frequency magnetron sputtering. The static magnetic properties and high frequency characteristics were investigated by measuring the hysteresis loops and microwave permeability spectra. The static magnetic results revealed that Co90Zr10 thin films prepared by oblique sputtering possessed a well-defined in-plane uniaxial magnetic anisotropy. It is found that the in-plane uniaxial magnetic anisotropy increased with the increasing oblique angle with a peak at 55° and then dropped rapidly above this angle. This behavior was qualitatively explained to be a result of the microstructure due to self-shadowing effect. Continuous modification of the resonance frequency in the range of 1.82–7.13GHz has been achieved, which is essential in high frequency applications of soft magnetic thin films.

Electromagnetic wave absorbing properties and hyperfine interactions of Fe—Cu—Nb—Si—B nanocomposites

The Fe—Cu—Nb—Si—B alloy nanocomposite containing two ferromagnetic phases (amorphous phase and nanophase phase) is obtained by properly annealing the as-prepared alloys. High resolution transmission electron microscopy (HR-TEM) images show the coexistence of these two phases. It is found that Fe—Si nanograins are surrounded by the retained amorphous ferromagnetic phase. Mössbauer spectroscopy measurements show that the nanophase is the D03-type Fe—Si phase, which is employed to find the atomic fractions of resonant 57Fe atoms in these two phases. The microwave permittivity and permeability spectra of Fe—Cu—Nb—Si—B nanocomposite are measured in the frequency range of 0.5 GHz–10 GHz. Large relative microwave permeability values are obtained. The results show that the absorber containing the nanocomposite flakes with a volume fraction of 28.59% exhibits good microwave absorption properties. The reflection loss of the absorber is less than −10 dB in a frequency band of 1.93 GHz–3.20 GHz.

Microwave permeability of single cobalt nanotube studied by micromagnetics simulations and generalized Snoek’s law

Microwave permeability spectra of single Co nanotube under equilibrium state have been studied by micromagnetics simulation. More than four obvious resonance peaks have been found (11.72, 24.20, 33.18 and 39.55 GHz). Such large resonance frequency cannot be found in other traditional magnetic materials. The configurations of magnetic moments along the nanotube have been simulated. The results show that the top end of nanotube has a “flow-out” pattern of magnetic moments configuration. The bottom end has a “flow-in” pattern of magnetic moments configuration. The magnetic moments within the main body of nanotube are aligned perfectly along the length of nanotube. The magnitude of natural resonance peak is strongly related to the volume fraction of a zone, which has the same orientation of magnetic moments. Large microwave permeability values have been found for single nanotube. The generalized Snoek’s law has been used to validate the micromagnetics simulations in this paper.

Evidence of an embedded vortex translation mode in flake-shaped ferromagnetic particle composites

A low-frequency resonance (sub-GHz) is observed in microwave permeability spectra of anisotropic flake-shaped ferromagnetic particle composites. The resonance frequency of this peak increases linearly with the saturation magnetization of flakes, their aspect ratio, and the amplitude of a perpendicular static magnetic field. In addition, this resonance becomes extinct for a perpendicular RF exciting magnetic field. These experimental features are reproduced by an analytical model of vortex dynamics which militates in favor of an assignment of this low-frequency signal as an embedded vortex translation mode within a multidomain magnetic structure.

Thermal stability of exchange-biased NiFe/FeMn multilayered thin films

A systematic study of the effect of ferromagnetic thickness on magnetic and microwave properties of exchange-biased NiFe/FeMn multilayered thin films was carried out with regards to thermal stability. The temperature-dependent microwave characteristics of the films were obtained from the near-field microwave microscopy technique and analysed based on Landau-Lifshitz-Gilbert equation. The complex microwave permeability spectra of the magnetic thin films up to 5 GHz in the temperature range from room temperature to 420 K were measured. It was found that thicker ferromagnetic layers helped to reduce the dependence of the magnetic properties on temperature, leading to better thermal stability. The saturation magnetization MS, dynamic magnetic anisotropy field HKdyn, and ferromagnetic resonance frequency fFMR were found to decrease with temperature, while the effective damping coefficient αeff was increased with temperature. We also investigate the rotational magnetic anisotropy field HKrot with temperature which gives a measure of the rotatable magnetization of the antiferromagnetic layers and its thermal stability.

Tuning the permeability spectra with a half-free ferromagnetic underlayer in (NiFe/IrMn)n exchange-biased multilayers

The influence of a half-free ferromagnetic underlayer on the static and microwave magnetic properties in [NiFe/IrMn]n exchange bias multilayer thin film system has been systematically investigated. By changing the thickness of the half-free ferromagnetic underlayer, the linewidth of the ferromagnetic resonance (FMR) in this system can be tuned from 0.9 to 2.4GHz. Theoretical fitting of the FMR frequencies based on the Landau–Lifshitz–Gilbert equation is also carried out to quantitatively identify the effective anisotropy fields and Gilbert damping parameters. The results provide an effective and flexible way to tailor the microwave permeability spectra and broaden the frequency linewidth toward the low frequency range in [ferromagnetic/antiferromagnetic]n exchange bias multilayer films system. This approach has potential application for tunable wideband high frequency noise filters.

Adjustable Microwave Properties in FeCoZr/Cu Multilayers

The FeCoZr/Cu multilayers were prepared by radio frequency sputtering. The static and microwave properties of these films were investigated by measuring the hysteresis loops and microwave permeability spectra. According to the static magnetic results, the multilayers were well in-plane uniaxial anisotropic samples with high saturation magnetization 1.7 T. The anisotropic field of these multilayer thin films can be adjusted from 18 Oe to 64 Oe by changing the thickness of Cu interlayer from 8.7 nm to 1.8 nm. As a consequence, the microwave permeability and resonance frequency can also be adjusted from 1.70 GHz to 2.88 GHz. This work might facilitate search for new materials with high permeability at high frequency.

Microwave absorption properties of Fe@Al 2O 3 nanoembedments prepared by mechanosynthesis

The iron nanoparticles embedded in alumina powder (Fe@Al 2O 3 nanoembedments) were prepared by a mechanochemical process. Their potential for microwave absorber is evaluated. The insulating embedment provides encapsulation and prevents oxidation and agglomeration of metal nanoparticles. The hysteresis loop of such nanoembedments at room temperature exhibits a superparamagnetic behavior, while the microwave permeability spectra show a multiresonance behavior. The maximum reflection loss can reach −21.4 dB at a higher frequency of ∼13.3 GHz as the thickness is 1.4 mm. The coexistence of superparamagnetic loss and multiresonant loss is responsible for microwave absorption. The Fe@Al 2O 3 nanoembedments may become attractive candidates for a new type of microwave absorber.

Efficient dynamic magnetization measurement in a Py/Ru/Py trilayer

It has previously been shown that the quantity called the "efficient dynamic magnetization", is a powerful tool for characterizing magnetic layers dedicated to microwave applications. It correlates the imaginary part of permeability and the magnetization distribution. This paper presents microwave permeability spectra of a Py/Ru/Py trilayer, which have been measured in the layer plane under an external magnetic static field (HDC) using a single coil cell. The efficient dynamic magnetization versus HDC was found to exhibit a significant decrease for 0<HDC<5 Oe, and it is demonstrated that this decrease was induced by an optic mode excitation.

Extrinsic damping contribution in soft magnetic thin films detected by permeability spectra

This work focuses on the identification of extrinsic damping contribution in FeCoN and FeCoSiN soft magnetic thin films by microwave permeability spectra measurements. The comparison of hysteresis loops shows that FeCoSiN thin film has a stronger in-plane uniaxial anisotropy. Through the analysis on the field-dependent frequency linewidth, the extrinsic damping contribution from two-magnon-scattering in FeCoN thin films is identified. The two-magnon-scattering damping contribution is greatly enhanced in FeCoSiN film due to the granular microstructure which brings about much more interface area between the two phases.

Effects of Nickel addition on the microwave permeability spectra of sputtered Fe–Co–Ni–B thin films

Abstract In order to develop the materials with high-frequency characteristics, the effects of Ni addition on the microwave permeability spectra of sputtered FeCoNiB thin films have been investigated in the range of 0.5–5 GHz by a shorted microstrip transmission line perturbation method. It is found that films with appropriate low Ni content exhibit excellent high-frequency characteristics resulting from the B segregation on grain boundaries: the real part of permeability at 0.5 GHz, the ferromagnetic resonance frequency, and the resistivity achieve 332, 3.16 GHz and 276 μΩ cm, respectively. Meanwhile, the degeneration of the soft magnetic properties and high-frequency characteristics occurs in the films with high Ni content, owing to the increase of metallic phase and anisotropy dispersion. As a result, appropriate increment of Ni content is of advantage to soft magnetic properties and high-frequency characteristics.

Microwave permeability spectra of sputtered Fe-Co-B soft magnetic thin films

Permeability characteristics of sputtered soft magnetic Fe4oCo4oB2o thin films are investigated in the range of 0.5 to 5 GHz by a shortened microstrip transmission line perturbation method. Excellent microwave permeability is achieved at 0.4 Pa argon pressure: f r is 3.32 GHz, the real and imaginary part of permeability at 0.5 GHz are 104 and 61, respectively. In addition, the thickness effect on permeability is also studied. The minimum damping can be achieved at the thinnest film. Different sources contributed to in-plane anisotropy are discussed briefly. The deviation between the peak frequency of the imaginary part and the zero-crossing frequency of the real part of permeability is also presented.

Sum rules and figures-of-merit on the microwave permeability of nanocrystalline microwires

The microwave permeability spectra of three nanocrystalline microwires were investigated, and dynamic magnetization M μ ( F) was determined from these spectra. An experimental verification of the theoretical prediction that this quantity was lower than the saturation magnetization was carried out, and it was further shown that the theoretical result provided straightforward guidelines for the conception of high-permeability materials, including successful tradeoffs between a higher resistivity and an increased saturation magnetization. M μ ( F) was determined to be an appropriate figure-of-merit for several applications, including high-frequency noise suppressors.

Microwave permeability spectra of flake-shaped FeCuNbSiB particle composites

The effective permeability of flake-shaped FeCuNbSiB particles/nonmagnetic matrix composition in high frequency was measured and calculated. In contrast to the relatively larger size and irregular shape particles, the flake particles have higher permeability. The results are attributed to the different magnetic loss mechanisms. According to the skin-effect criterion, we find that the magnetic loss in flake particles is mainly caused by the natural resonance, compared with the eddy current effect in the larger size and irregular shape particles. Using the shape anisotropy, the flake soft magnetic particles overcome the difficulty of the relatively small intrinsic anisotropies and increase the natural resonant frequencies to the gigahertz range, leading to the higher real part and imaginary part of the permeability. The resonance peak of flake particles was simulated using the combination of the Landau–Lifshitz–Gilbert equation and Bruggeman’s effective medium theory considering a random spatial distribution of magnetic easy axes. Our theory simulation agrees well with the experimental data.

Temperature dependence of magnetic properties of AF-biased CoFe films with high FMR

We investigate the temperature dependence of static and dynamic magnetic properties of AF/F/AF multilayers consisting in NiMn as AF-layer and Co/sub 90/Fe/sub 10/, Co/sub 50/Fe/sub 50/ and Co/sub 35/Fe/sub 65/ as F-layer, respectively. The T-dependences of the hysteresis loops have been analyzed in relation with the corresponding microwave permeability spectra. The results indicate a lowering of both the exchange bias (Hex) and the anisotropy field (Hk dc) above 150/spl deg/C, in agreement with blocking temperature considerations from literature. However, microwave characterizations show better high temperature stability, with a shift of ferromagnetic resonance frequency less than 20% up to 300/spl deg/C. This reveals a strong discrepancy between the anisotropy field from the static and dynamic measurements including the T-dependence. Finally, this work points out unexpected excellent temperature stability up to 300/spl deg/C proving that such multilayers are available for future use in RF devices at very high frequencies.

Secondary peaks on microwave permeability spectra of soft ferromagnetic thin films with in-plane anisotropy

Complex permeability spectra of CoNbZr thin films have been measured up to 4GHz by a single coil pertubation technique. In addition to the well-known ferromagnetic resonance, multiple resonant modes have been evidenced in the increasing branches of the spectra. The number of “secondary peaks” observed depends on the sample thickness. Their resonance frequencies follow a nonlinear dispersion law versus the ratio of the mode number over the sample thickness with a power factor close to 1.5.

Microwave permeability of amorphous ferromagnetic glass-coated microwires from 150 K to 450 K

Microwave permeability spectra of ferromagnetic glass-coated microwires at room temperature have already been studied. Using a new setup that we have recently developed, permeability spectra of ferromagnetic microwire at various temperatures are presented. CoFeSiB soft ferromagnetic microwires are studied from 150 K to 450 K, showing large changes in their permeabilities between 30 MHz and 3 GHz.