20 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



The loss characteristics of different ferrites as a function of the ap- 

 phed magnetic field differed distinctly from each other. Some ferrites, 

 such as manganese zinc ferrite showed extremely high loss which was 

 associated with the imaginary part of the dielectric constant. This loss 

 was not affected by the application of a magnetic field but remained 

 substantially constant as the field was applied. However, as the field 

 approached that necessary for ferromagnetic resonance, the total power 

 absorbed by the ferrite increased, since the positive circularly polarized 

 component was almost completely absorbed by the sample. In fact by 

 measuring the ellipticity of the transmitted wave, it is possible to com- 

 pute the difference between the absorption of the positive and negative 

 circularly polarized components. This has been done for Sample No. 1 

 and the result is indicated in Fig. 9. If the curve were continued to 

 higher fields, it would represent the shape of the ferromagnetic resonance 

 absorption line. 



Some ferrites, such as Ferramic G, showed an almost zero dielectric 

 loss but on the other hand caused an extremely large absorption at 9000 

 megacycles due to magnetic losses. The major contributions to magnetic 

 loss at this frequency should be either losses associated with a domain 

 wall relaxation or ferromagnetic resonance absorption due to anisotropy 

 fields. Unequivocal data can be obtained by the above techniques to 

 identify which loss is predominant. If the loss were due to domain wall 

 relaxation (or resonance) it would absorb both the negative and positive 

 circularly polarized components equally. Thus as the magnetic field 

 was apphed and as the ferrite became saturated, the losses in both 

 components should decrease as the domain walls disappeared. However, 



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400 800 1200 1600 2000 2400 2800 3200 3600 4000 



MAGNETIC FIELD IN OERSTEDS 



Fig. 9 — Ferromagnetic resonance absorption curve determined by measuring 

 the ellipticity of a wave transmitted through a cylinder of ferrite in a waveguide. 



