Microwave permeability of amorphous Co₆₇Fe₇B₂₆ films deposited on a flexible substrate was studied in a wide range of film thicknesses up to 1.40 μm. Microwave permeability measurements were carried out using the coaxial technique in the frequency range from 0.1 to 10 GHz. It was found that both the static permeability and the ferromagnetic resonance frequency depend weakly on the film thickness. Analysis of the microwave data showed that the studied films possess in-plane magnetic anisotropy. The influence of the skin effect on the frequency dependence of the microwave permeability was modeled using an analytical approach. It was demonstrated that the decrease in the peak of the imaginary part of the microwave permeability with film thickness growth is related to the skin effect. The results obtained may be useful for microwave applications of soft magnetic CoFeB films.

The microwave permeability of composites containing microsized gadolinium powder in paraffin wax was studied as a function of frequency, temperature and gadolinium fraction for a series of composites with a powder volume fraction of 5% to 50%. The constitutive parameters of the composites were measured by the Nicolson–Ross–Weir technique in a standard 7 × 3 mm coaxial line in the frequency range of 0.1 to 10 GHz and the temperature range of 5 to 26 °C. In the indicated ranges, the permittivity was independent of frequency and temperature, and the real part of the permittivity only depended on the gadolinium powder volume fraction. It was found that the peak of the magnetic losses shifts towards lower frequencies with an increase in temperature. The Curie temperature of the composites found from the temperature dependence of the static permeability was close to 15 °C, being practically independent of the gadolinium volume fraction. To retrieve the intrinsic permeability of the filler particles, the Odelevsky mixing rule was used. The measured dependence of the static permittivity on the gadolinium volume fraction was in good agreement with the fitting by the Odelevsky mixing rule. Using the values of the percolation threshold and the depolarization factor obtained as a result of the fitting of the static permittivity, the frequency dependence of the intrinsic permeability of the filler particles was retrieved. The temperature effect on the intrinsic permeability was also analyzed. The obtained results may be useful for designing microwave devices, including temperature-tunable microwave screens and sensors.

A broadband method for measuring the complex permeability of thin magnetic films using a short-circuited microstrip fixture is presented. The method is based on full one-port offset-short calibration implemented directly in the fixture with a movable shorting wall, reducing sensitivity to coaxial-to-strip transition imperfections and eliminating the need for its precise optimization. Field-dependent normalization to the empty fixture reduces systematic errors from the external magnetic field, and a correction for residual saturated permeability improves retrieval accuracy. The method was validated on Co, supermalloy, and FeCo films on flexible PET substrates. Retrieved spectra agreed well with reference coaxial data and with the spectrum reconstructed from static magnetic measurements. In the present implementation, broadband spectra were obtained from 0.1 to 20 GHz with no significant systematic distortion, indicating that the proposed approach is suitable for accurate broadband characterization of thin magnetic films without reference standards or precise optimization of the coaxial-to-strip transition.