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Microwave ferrites and dielectrics
Ferrite garnets with narrow and ultra-narrow ferromagnetic resonance line width
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Microwave ferrites and dielectricsTerms

Terms and definitions concur with IEC Recommendations, 50(901), 50 (901A), 556.
 
SYMBOLS
 
4πMs
Saturation magnetization
G
ΔH
FMR line width
Oe
ε
Real part of complex dielectric constant
 
tgδε
Dielectric loss tangent
 
geff
Lande factor
 
Tc
Curie temperature
C
ΔHk
Spin-wave line width
Oe
HAeff
Effective anisotropy field
kOe
αMs
Temperature coefficient of
saturation magnetization
%C-1
Hc
Coercive force strength
Oe
Br
Remanent magnetic flux density
G
W
Water absorption
%
 
 
 
1. Saturation magnetization, 4πMs
- the highest attainable magnetization value (magnetic moment of material volume) for particular material at given temperature.
    The value of saturation magnetization is given by Ms=mspa/P (G), where:
ms - magnetic moment of  test specimen (the sphere 1.0 ... 1.5 mm diameter);
ra appearing material density;
P - mass of test specimen. Magnetic moment is measured by vibrating sample self-compensating method, at constant temperature in direct current magnetic field of 8 kOe. The relative error of  Ms value with probability of 0.95 is no more than 2.5%.
 
2. Ferromagnetic resonance line ­width, DH at level - 3dB
- the difference between two magnetic field strength values at which the power absorbed by ferrite material is half the maximum absorption. The measurement of ferromagnetic resonance linewidth and effective Lande factor geff is executed by the resonant cavity method at 9.4 GHz on spherical specimens. The field value corresponding to maximum absorption is the resonant value (Hr) and used in calculation of  geff:
geff=2pfo/kHr , where:
fo - FMR frequency (s-1);  
k=e/2mc   (e and m  are electrical charge and mass of electron, c - velocity of light);
Hr - resonance magnetic field (Oe).
The DH measurement accuracy is +(5+2/DH)%.
 
3. Dielectric loss tangent, tgde
     ee'+je'' , tgde =e/e, where: e - real part of the permit­tiv­ity;  e - imaginary part of the permittivity. Both real and imaginary parts of permittivity are determined by standard TE10n (n is odd 3 or greater) cavity resonant method with using specimen rods (1.12 x 1.12 x 18) mm, at frequency 9.4 GHz.
where: e'- real part of the permittivity; e" imaginary part of the permittivity;
The measurement complex dielectric permittivity is executed in accordance of the Standard International Elektrotehnial Commission (the publication 556, 1982.). Cylindrical  TM010 on the frequency 9,4 GHz and checking sample by size 1,12x1,12x18 mm are used.
The measurements accuracy are: e ≤ 3% ; e ≤ (10+ 0.06/e)%.
 
4. Effective anisotropy field of polycrystalline materials, HAeff
The measurement of the anisotropy field is conducted by resonance method on sphere  within the range of frequencies 53 - 78 GHz or on - plates within the range of 78 - 120 GHz.
The Aeff measurement accuracy is :  (5+5DH/HAeff)%.
 
5. Spin-wave resonance line width, DHk
- defines dissipative properties of the materials at high microwave power. It is defined by equation:
DHk = (4pMsg/2pf)hCmin, where:
hCmin - minimal microwave magnetic field amplitude at the critical power level corresponding to appearance of non-linear phenomena in ferrite (Oe);
g - giromagnetic ratio (Oe-1s-1);
f - frequency of signal (Hz). The spin-wave linewidth is measured on 1...2 mm diameter sphere in a cylindrical cavity using parallel pumping tech­nique. The measurement is performed either in hollow TE10n cavity or dielectric cavity, depending on diameter of sphere and expected  DHk value.
The microwave signal 9.4 GHz is fed by pulse duration of 1ms, 3ms  or 5ms  with on-off time ratio q=2500.
The  measurement accuracy is +15%.
 
6. Hysteresis loop characteristics, Br, Hc
- characteristics of hysteresis loop of materials are measured by induction method on toroidal specimens. The test is executed in quasistationary regime of remagnetization at 209 Hz in applied field of Hm=5Hc.
The measurement accuracy of Br, Hc, is 5%.
 
 


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