1342 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



N N N N N N 



s s s s s s 



WITH FIELD APPLIED 



NO FIELD APPLIED 



Fig. 6 — A typical domain wall pattern showing the movement of the wall in 

 response to the application of an external magnetic field. 



many ways like an internal field tending to keep the magnetization of 

 the constituent crystallites along one of the axes of easy magnetization. 

 In most ferrites there are four such axes and since the magnetization can 

 be in either direction along any one of these, there are eight directions of 

 easy magnetization. When a field is applied the effective internal field 

 is roughly the vector sum of the applied field and the anisotropy field 

 associated with the nearest axis. In a polycrystalline ferrite composed of 

 many randomly oriented crystallites it is evident, therefore, that the 

 internal field varies from point to point in the body so that the resonance 

 absorption line is broadened by an amount proportional to the mag- 

 nitude of the anisotropy field. A similar broadening can arise from 

 magnetostriction due to fields arising from varying strains throughout 

 the polycrystalline ferrite, and non-uniform internal demagnetizing fields 

 due to the shape of the constituent particles or crystallites can like^vise 

 broaden the resonance line. Since a broad resonance line results in el- 

 lipticity of the transmitted wave it is desirable to use a ferrite having low 

 anisotropy. 



Curve By Fig. 5 



Frequently a loss is observed at low fields as indicated in Fig. 5 by 

 Curve B. Neglecting waveguide effects this hump is S3nnmetricaf so 

 that it evidently depends on a phenomenon which affects both circular 

 components equally. It is generally agreed that it depends upon the 

 existence of domain walls within the material since it usually disappears 

 as soon as the body is magnetized. However, there is some question as 

 to the specific mechanism involved. 



• Fox and Weiss, Revs. Mod. Phys., 26, p. 262, Jan., 1953. 



