Corresponding author: Vladimir G. Kostishin (drvgkostishyn@mail.ru)
In this work we have considered metrological problems and measurement of magnetic parameters and presented methods of measuring effective magnetic anisotropy field
The methods have been tested for polycrystalline specimens of hexagonal barium and strontium ferrites with nominal composition or complex substituted and having high magnetic texture. The measurement results have been compared with those obtained using conventional measurement methods and spherical specimens. Our methods prove to be highly accurate and reliable.
Microwave electronics are currently the main development trend of the entire electronics industry [
The most promising microwave electronics materials are hexagonal ferrites in the form of single crystals or textured polycrystals [
The demand for highquality magnetically uniaxial hexagonal ferrites for microwave applications in electronics stimulates the improvement of existing and the development of new hexagonal ferrite technologies and studies of their properties [
The main parameters of ferromagnetic resonance
General problems of material properties measurement in microwave electromagnetic range were reported earlier [
Below we consider methods for
effective magnetic anisotropy field HAeff: 10–23 and 28–40 kE;
FMR bandwidth ∆ Н: 0.5–5 kE.
The method is based on the dependence of the
The wave impedance of the hexagonal ferrite plates (ε_{f} = 13÷18) was matched with the wave impedance of the free space using planeparallel quartz plates (ε_{q} = 3.8÷3.9) located at both sides of the hexagonal ferrite plates. The thickness of the quartz plates was λ_{q}/4 where λ_{q} is the wavelength in the quartz plate at the measurement frequency. The specimen and the quartz plates were placed between two horn waveguide transitions one of which generated a quasiplanar electromagnetic wave and the other was excited by the quasiplanar electromagnetic wave after passage through the specimen.
The linear horn aperture size of horn waveguide transitions should be at least 3λ_{0} where λ_{0} is the wavelength in the free space at the measurement frequency and be matched with the free space and the electromagnetic source. The voltage standing wave ratio of the horn waveguide transition entrance is max. 1.1).
Since the test specimen was demagnetized it could not excite a secondary wave and therefore the wave attenuated while passing through the specimen only due to the electromagnetic absorption at natural
The
Model of demagnetized hexagonal ferrite plate.
Therefore
where γ is the gyromagnetic ratio and 4π
The ferromagnetic resonance bandwidth ∆
where
The method was tested for the 3mm wave range using a panoramic device for voltage standing wave ratio and attenuation measurement Rem2.648.020 developed at Shokin NPP Istok JSC. The measurement results for polycrystalline hexagonal ferrite plates with
The panoramic device for voltage standing wave ratio and attenuation measurement R2124M for 3mm wave range (working frequency range 78.33–118.1 GHz) was used as a basis for the experimental unit for
The measurement unit included the panoramic device for voltage standing wave ratio and attenuation measurement R2124M and the measurement module developed by the Authors which is connected into the measurement circuit.
The general appearance of the panoramic device for voltage standing wave ratio and attenuation measurement R2124M is shown in Fig.
General appearance of R2124M panoramic voltage standing wave ratio and attenuation meter.
Schematic of R2124M device.
The measurement module included a platform and two horn waveguide transitions (the waveguide crosssection is 1.2 × 2.4 mm^{2} and the horn aperture is 10 × 10 or 14 × 14 mm^{2}) with the entrance voltage standing wave ratio being max. 1.1 in the working frequency range of the R2124M meter.
Schematic of the measurement module with the test specimen and the matching quartz plates installed between horn waveguide transitions is shown in Fig.
Schematic of measuring module: (
The experimental unit had the following parameters:
working frequency range 78.33–118.1 GHz;
measured parameter ranges: effective anisotropy field 28–40 kE, magnetic resonance bandwidth 0.3–5.0 kE;
test specimen shape: planeparallel rectangular (or round) plate with transverse sizes of at least 20 × 20 mm 2 (the diameter being at least 20 mm) and a thickness of 0.2–1.0 mm;
matching quartz plate dimensions: transverse sizes min. 20 × 20 mm 2, thickness λ q/4 (λ q being the wavelength in quartz at the measurement frequency);
measurement error range at 0.95 confidence: relative error of effective anisotropy field measurement ∆ HAeff is max. ±5%; relative error of FMR bandwidth measurement (∆ H) is max. ±20%;
operation conditions: ambient temperature (+10 ÷ +35) °C; relative humidity at 25 °C: 80%; atmospheric pressure 86÷106 kPa.
The saturation magnetization is measured using an AMT4 automatic hysteresis recorder of Mianyang Shuangji Electronic Co. Ltd. (relative error of saturation magnetization measurement ±1%).
We studied the possibility of measuring effective anisotropy field and
Broadband measurements were carried out using an Agilent N5227A vector circuit analyzer as an
The polycrystalline
The measurement unit included an Agilent N5227A vector circuit analyzer (working frequency range 10 MHz – 67 GHz), an Anritsu 3680V coaxial microstrip measurement module and an
The measurement sequence was as follows.
The MTL on an aluminum substrate is installed into the measuring module connected to the circuit analyzer, and its transmission ratio is normalized (equalized).
The test specimen in the form of a prism sized max. 0.5 × 0.5 × (0.15–0.25) mm 3 is placed onto the MTL.
The frequencies are measured at the magnetic resonance band positions corresponding to the half of absorbed energy (f1 and f2).
The resonance frequency fr, the effective anisotropy field HAeff and the magnetic resonance bandwidth ∆ H are calculated using Eqs (3), (1) and (2), respectively. When assessing the effect of demagnetizing factors on the FMR resonance frequency we replaced the prism for an oblate inellipsoid of revolution.
If the specimen is magnetized and the measurements are carried out with an external magnetic field then the ∆
where γ is the gyromagnetic ratio, 4π
where ϑ is the ellipsoid height to diameter ratio).
If the specimen is magnetized the measurements are carried out without an external magnetic field:
where 4π
If the specimen is demagnetized then:
where ζ is the coefficient determined by the domain structure of the demagnetized test specimen.
When calculating
When calculating
The experimental unit had the following parameters:
– working frequency range 20–67 GHz;
– measured parameter ranges: effective anisotropy field 10–23 kE, magnetic resonance bandwidth 0.1–5 kE;
test specimen shape: planar rectangular with a square base and linear sizes of max. 0.5 × 0.5 mm 2 and a thickness of 0.15–0.25 mm, the texture axis being perpendicular to the prism base;
measurement error range at 0.95 confidence: relative error of HAeff measurement (∆ HAeff) is max. ±5%; relative error of ∆ H measurement ∆(∆ H) is max. ±20%;
operation conditions: ambient temperature 10–35 °C; relative humidity at 25 °C: 80%; atmospheric pressure 86÷106 kPa.
The saturation magnetization was measured using an AMT4 automatic hysteresis recorder of Mianyang Shuangji Electronic Co. Ltd. (relative error of saturation magnetization measurement ±1%).
Figure
Interface with typical
The diameter of the test planeparallel demagnetized plates of barium
Results of






88.8  102.8  
97.2  107.5  
92.9  105.15  
4π 
1800  1400 
32.0  36.5  
Δ 
3.0  1.68 
Typical
The results of frequency measurements (
Results of HAeff and ∆H measurement for
Parameter  Specimen ( 


HB25  HS81  
41.18  45.88  
53.32  56.04  
Δ 
12.14  10.16 
47.25  51.00  
17.8  19.22  
Δ 
4.34  3.63 
4π 
3200  3500 
Our methods of measuring effective magnetic anisotropy field
Testing of the methods for measuring
We showed that our methods are effective in the measurement of electromagnetic parameters of magnetically uniaxial hexagonal ferrites used in microwave electronics and they will speed up the implementation of millimeter wave range devices on substrates made from these materials.
This work was performed within the Hexagonal Ferrite R&D Project funded by Shokin NPP Istok JSC with financial support from the Ministry of Education and Science of the Russian Federation under Subvention Agreement No. 14.575.21.0030 as of June 27, 2014 (RFMEFI57514X0030).